Built TclTLS 1.7.21 on MacOS 10.6, against Tcl 8.6.10 and OpenSSL 1.1.1g.
Building went okay (once I figured out I need to make sure gen_dh_params 
finds up the right version of the openssl program), and make test works.

Then I try the following minimal https operation:

% package require tls
1.7.21
% package require http
2.9.1
% http::register https 443 [list ::tls::socket -autoservername true -require true -cafile /usr/local/ssl/cert.pem]
443 {::tls::socket -autoservername true -require true -cafile /usr/local/ssl/cert.pem}
% set tok [http::geturl https://www.tcl-lang.org/]

Under tclsh, that works fine. 
Under wish, it segfaults! Consistently.

More detailed breakdown, with debug build of tcltls:

----------- Begin output:
% package require tls
./tls.c:1779:Tls_Init():Called
./tls.c:1897:TlsLibInit():Called
./tlsBIO.c:53:BIO_new_tcl():BIO_new_tcl() called
./tlsBIO.c:66:BIO_new_tcl():Asked to setup a NULL state, just creating the initial configuration
1.7.21
% package require http
2.9.1
% http::register https 443 [list ::tls::socket -autoservername true -require true -cafile /usr/local/ssl/cert.pem]
443 {::tls::socket -autoservername true -require true -cafile /usr/local/ssl/cert.pem}
% set tok [http::geturl https://www.tcl-lang.org/]
./tls.c:759:ImportObjCmd():Called
./tls.c:1093:CTX_Init():Called
/usr/local/bin/wish: line 2: 67253 Segmentation fault      "$(dirname $0)/../../../Library/Frameworks/Tk.framework/Versions/8.6/Resources/Wish.app/Contents/MacOS/Wish" "$@"
----------- End output.

----------- Begin crash report:
Process:         Wish [67253]
Path:            /usr/local/bin/../../../Library/Frameworks/Tk.framework/Versions/8.6/Resources/Wish.app/Contents/MacOS/Wish
Identifier:      com.tcltk.wish
Version:         8.6.10 (8.6.10)
Code Type:       X86-64 (Native)
Parent Process:  sh [67251]

Date/Time:       2020-08-19 11:21:01.998 +0200
OS Version:      Mac OS X 10.6.8 (10K549)
Report Version:  6

Interval Since Last Report:          84517688 sec
Crashes Since Last Report:           808
Per-App Interval Since Last Report:  62722 sec
Per-App Crashes Since Last Report:   5
Anonymous UUID:                      1739C455-2439-487D-9ED0-2084ED6CAF3F

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000000
Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Thread 0 Crashed:  Dispatch queue: com.apple.main-thread
0   libSystem.B.dylib             	0x00007fff870ed7ee pthread_rwlock_wrlock + 50
1   libcrypto.1.1.dylib           	0x00000001150661ec CRYPTO_atomic_add + 44
2   libcrypto.1.1.dylib           	0x0000000114f77041 DH_up_ref + 33
3   libcrypto.1.1.dylib           	0x0000000114fff028 EVP_PKEY_set1_DH + 104
4   libssl.1.1.dylib              	0x0000000114d454f2 ssl3_ctx_ctrl + 1538
5   tcltls.dylib                  	0x00000001006351c3 ImportObjCmd + 2963 (.tls.c:1265)
6   Tcl                           	0x000000010018496f Tcl_ListMathFuncs + 3856
7   Tcl                           	0x000000010017e279 TclNRRunCallbacks + 58
8   Tcl                           	0x0000000100202fa3 Tcl_RecordAndEvalObj + 499
9   Tcl                           	0x0000000100203003 Tcl_RecordAndEval + 70
10  Tk                            	0x000000010002c91a TkPointerEvent + 19546
11  Tcl                           	0x000000010020d98c Tcl_NotifyChannel + 219
12  Tcl                           	0x0000000100272f3d Tcl_Sleep + 923
13  Tcl                           	0x0000000100226605 Tcl_ServiceEvent + 147
14  Tcl                           	0x00000001002268f5 Tcl_DoOneEvent + 314
15  Tk                            	0x000000010001ee29 Tk_MainLoop + 24
16  Tk                            	0x000000010002d24a Tk_MainEx + 2067
17  Wish                          	0x0000000100005141 0x100000000 + 20801
18  Wish                          	0x000000010000507c 0x100000000 + 20604

Thread 1:  Dispatch queue: com.apple.libdispatch-manager
0   libSystem.B.dylib             	0x00007fff870a5c0a kevent + 10
1   libSystem.B.dylib             	0x00007fff870a7add _dispatch_mgr_invoke + 154
2   libSystem.B.dylib             	0x00007fff870a77b4 _dispatch_queue_invoke + 185
3   libSystem.B.dylib             	0x00007fff870a72de _dispatch_worker_thread2 + 252
4   libSystem.B.dylib             	0x00007fff870a6c08 _pthread_wqthread + 353
5   libSystem.B.dylib             	0x00007fff870a6aa5 start_wqthread + 13

Thread 2:
0   libSystem.B.dylib             	0x00007fff870d0932 select$DARWIN_EXTSN + 10
1   Tcl                           	0x0000000100273f38 Tcl_InitNotifier + 1582
2   libSystem.B.dylib             	0x00007fff870c5fd6 _pthread_start + 331
3   libSystem.B.dylib             	0x00007fff870c5e89 thread_start + 13

Thread 0 crashed with X86 Thread State (64-bit):
  rax: 0x0000000000000000  rbx: 0x0000000000000000  rcx: 0x0000000000000000  rdx: 0x00007fff5fbfc5fc
  rdi: 0x0000000000000000  rsi: 0x0000000000000001  rbp: 0x00007fff5fbfc5b0  rsp: 0x00007fff5fbfc570
   r8: 0x0000000114f14aa0   r9: 0x00000001004fc0a4  r10: 0x0000000000000015  r11: 0x0000000100495c80
  r12: 0x00000001004977a8  r13: 0x0000000000000001  r14: 0x00007fff70c83cc0  r15: 0x0000000100878a10
  rip: 0x00007fff870ed7ee  rfl: 0x0000000000010246  cr2: 0x0000000000000000

Binary Images:
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    0x7fff86cae000 -     0x7fff86ccffe7  libPng.dylib ??? (???) <D8EC7740-EE32-865A-2F75-C9EDE2135510> /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ImageIO.framework/Versions/A/Resources/libPng.dylib
    0x7fff86cd0000 -     0x7fff86d3afe7  libvMisc.dylib 268.0.1 (compatibility 1.0.0) <AF0EA96D-000F-8C12-B952-CB7E00566E08> /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libvMisc.dylib
    0x7fff8708c000 -     0x7fff8724dfef  libSystem.B.dylib 125.2.11 (compatibility 1.0.0) <9AB4F1D1-89DC-0E8A-DC8E-A4FE4D69DB69> /usr/lib/libSystem.B.dylib
    0x7fff8724e000 -     0x7fff87275ff7  libJPEG.dylib ??? (???) <08758593-6436-B29E-1DA8-F15597835EC1> /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ImageIO.framework/Versions/A/Resources/libJPEG.dylib
    0x7fff87276000 -     0x7fff87277ff7  com.apple.audio.units.AudioUnit 1.6.7 (1.6.7) <49B723D1-85F8-F86C-2331-F586C56D68AF> /System/Library/Frameworks/AudioUnit.framework/Versions/A/AudioUnit
    0x7fff8741a000 -     0x7fff87427fe7  libCSync.A.dylib 545.0.0 (compatibility 64.0.0) <1C35FA50-9C70-48DC-9E8D-2054F7A266B1> /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/CoreGraphics.framework/Versions/A/Resources/libCSync.A.dylib
    0x7fff875e9000 -     0x7fff87666fef  libstdc++.6.dylib 7.9.0 (compatibility 7.0.0) <35ECA411-2C08-FD7D-11B1-1B7A04921A5C> /usr/lib/libstdc++.6.dylib
    0x7fff87667000 -     0x7fff876a8fff  com.apple.SystemConfiguration 1.10.8 (1.10.2) <78D48D27-A9C4-62CA-2803-D0BBED82855A> /System/Library/Frameworks/SystemConfiguration.framework/Versions/A/SystemConfiguration
    0x7fff87713000 -     0x7fff87773fe7  com.apple.framework.IOKit 2.0 (???) <4F071EF0-8260-01E9-C641-830E582FA416> /System/Library/Frameworks/IOKit.framework/Versions/A/IOKit
    0x7fff87774000 -     0x7fff87831fff  com.apple.CoreServices.OSServices 359.2 (359.2) <BBB8888E-18DE-5D09-3C3A-F4C029EC7886> /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/OSServices.framework/Versions/A/OSServices
    0x7fff878fa000 -     0x7fff87ab8fff  libicucore.A.dylib 40.0.0 (compatibility 1.0.0) <97A75BFB-0DB6-6F44-36B0-97B7F7208ABB> /usr/lib/libicucore.A.dylib
    0x7fff87c9c000 -     0x7fff87cdafe7  libFontRegistry.dylib ??? (???) <395D7C0D-36B5-B353-0DC8-51ABC0B1C030> /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ATS.framework/Versions/A/Resources/libFontRegistry.dylib
    0x7fff87d37000 -     0x7fff88731ff7  com.apple.AppKit 6.6.8 (1038.36) <4CFBE04C-8FB3-B0EA-8DDB-7E7D10E9D251> /System/Library/Frameworks/AppKit.framework/Versions/C/AppKit
    0x7fff88732000 -     0x7fff88848ff7  libxml2.2.dylib 10.3.0 (compatibility 10.0.0) <3814FCF9-92B9-A6AB-E76A-F7021894AA3F> /usr/lib/libxml2.2.dylib
    0x7fff88849000 -     0x7fff888fefe7  com.apple.ink.framework 1.3.3 (107) <8C36373C-5473-3A6A-4972-BC29D504250F> /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/Ink.framework/Versions/A/Ink
    0x7fff8894a000 -     0x7fff89154fe7  libBLAS.dylib 219.0.0 (compatibility 1.0.0) <2F26CDC7-DAE9-9ABE-6806-93BBBDA20DA0> /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
    0x7fff89398000 -     0x7fff893e1fef  libGLU.dylib ??? (???) <B0F4CA55-445F-E901-0FCF-47B3B4BAE6E2> /System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGLU.dylib
    0x7fff89583000 -     0x7fff89587ff7  libmathCommon.A.dylib 315.0.0 (compatibility 1.0.0) <95718673-FEEE-B6ED-B127-BCDBDB60D4E5> /usr/lib/system/libmathCommon.A.dylib
    0x7fff8958e000 -     0x7fff89662fe7  com.apple.CFNetwork 454.12.4 (454.12.4) <C83E2BA1-1818-B3E8-5334-860AD21D1C80> /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/CFNetwork.framework/Versions/A/CFNetwork
    0x7fff8975c000 -     0x7fff8975cff7  com.apple.vecLib 3.6 (vecLib 3.6) <96FB6BAD-5568-C4E0-6FA7-02791A58B584> /System/Library/Frameworks/vecLib.framework/Versions/A/vecLib
    0x7fff89798000 -     0x7fff89798ff7  com.apple.Accelerate.vecLib 3.6 (vecLib 3.6) <4CCE5D69-F1B3-8FD3-1483-E0271DB2CCF3> /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/vecLib
    0x7fff89b74000 -     0x7fff89c04fff  com.apple.SearchKit 1.3.0 (1.3.0) <45BA1053-9196-3C2F-2421-AFF5E09627CC> /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/SearchKit.framework/Versions/A/SearchKit
    0x7fff89e43000 -     0x7fff89e47ff7  libCGXType.A.dylib 545.0.0 (compatibility 64.0.0) <DB710299-B4D9-3714-66F7-5D2964DE585B> /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/CoreGraphics.framework/Versions/A/Resources/libCGXType.A.dylib
    0x7fff89eb1000 -     0x7fff89eb7ff7  com.apple.DiskArbitration 2.3 (2.3) <AAB5CC56-334A-3C60-3C27-54E8F34D754E> /System/Library/Frameworks/DiskArbitration.framework/Versions/A/DiskArbitration
    0x7fff89ec6000 -     0x7fff89ffbfff  com.apple.audio.toolbox.AudioToolbox 1.6.7 (1.6.7) <F4814A13-E557-59AF-30FF-E62929367933> /System/Library/Frameworks/AudioToolbox.framework/Versions/A/AudioToolbox
    0x7fff89ffc000 -     0x7fff8a012fe7  com.apple.MultitouchSupport.framework 207.11 (207.11) <8233CE71-6F8D-8B3C-A0E1-E123F6406163> /System/Library/PrivateFrameworks/MultitouchSupport.framework/Versions/A/MultitouchSupport
    0x7fff8a013000 -     0x7fff8a01afff  com.apple.OpenDirectory 10.6 (10.6) <4FF6AD25-0916-B21C-9E88-2CC42D90EAC7> /System/Library/Frameworks/OpenDirectory.framework/Versions/A/OpenDirectory
    0x7fff8a01b000 -     0x7fff8a032fff  com.apple.ImageCapture 6.1 (6.1) <79AB2131-2A6C-F351-38A9-ED58B25534FD> /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/ImageCapture.framework/Versions/A/ImageCapture
    0x7fff8a056000 -     0x7fff8a106fff  edu.mit.Kerberos 6.5.11 (6.5.11) <085D80F5-C9DC-E252-C21B-03295E660C91> /System/Library/Frameworks/Kerberos.framework/Versions/A/Kerberos
    0x7fff8a111000 -     0x7fff8a13cff7  libxslt.1.dylib 3.24.0 (compatibility 3.0.0) <3630A97F-55C1-3F34-CA63-3847653C9645> /usr/lib/libxslt.1.dylib
    0x7fff8a13d000 -     0x7fff8a160fff  com.apple.opencl 12.3.6 (12.3.6) <42FA5783-EB80-1168-4015-B8C68F55842F> /System/Library/Frameworks/OpenCL.framework/Versions/A/OpenCL
    0x7fff8a17d000 -     0x7fff8a182fff  libGIF.dylib ??? (???) <3BAD0DE8-8151-68B0-2244-A4541C738972> /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ImageIO.framework/Versions/A/Resources/libGIF.dylib
    0x7fff8a183000 -     0x7fff8a199fef  libbsm.0.dylib ??? (???) <0321D32C-9FE1-3919-E03E-2530A0C1191B> /usr/lib/libbsm.0.dylib
    0x7fff8a1f9000 -     0x7fff8a1fcff7  libCoreVMClient.dylib ??? (???) <75819794-3B7A-8944-D004-7EA6DD7CE836> /System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libCoreVMClient.dylib
    0x7fff8a1fd000 -     0x7fff8a237fff  libcups.2.dylib 2.8.0 (compatibility 2.0.0) <4F2A4397-89BD-DEAC-4971-EE838FFA0964> /usr/lib/libcups.2.dylib
    0x7fff8a238000 -     0x7fff8a24afe7  libsasl2.2.dylib 3.15.0 (compatibility 3.0.0) <30FE378B-99FE-8C7C-06D0-A3AA0A0A70D4> /usr/lib/libsasl2.2.dylib
    0x7fff8a267000 -     0x7fff8a269fff  com.apple.print.framework.Print 6.1 (237.1) <CA8564FB-B366-7413-B12E-9892DA3C6157> /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/Print.framework/Versions/A/Print
    0x7fff8a4b1000 -     0x7fff8a5d0ff7  libcrypto.0.9.8.dylib 0.9.8 (compatibility 0.9.8) <0CE8D59B-D0C7-1DCE-3654-37F27F61BEFA> /usr/lib/libcrypto.0.9.8.dylib
    0x7fff8a67b000 -     0x7fff8a7b9fff  com.apple.CoreData 102.1 (251) <9DFE798D-AA52-6A9A-924A-DA73CB94D81A> /System/Library/Frameworks/CoreData.framework/Versions/A/CoreData
    0x7fff8a7ba000 -     0x7fff8a7cbff7  libz.1.dylib 1.2.3 (compatibility 1.0.0) <97019C74-161A-3488-41EC-A6CA8738418C> /usr/lib/libz.1.dylib
    0x7fff8a7d5000 -     0x7fff8a7d8ff7  com.apple.securityhi 4.0 (36638) <AEF55AF1-54D3-DB8D-27A7-E16192E0045A> /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/SecurityHI.framework/Versions/A/SecurityHI
    0x7fff8a7d9000 -     0x7fff8a7d9ff7  com.apple.Cocoa 6.6 (???) <C69E895A-1C66-3DA9-5F63-8BE85DB9C4E1> /System/Library/Frameworks/Cocoa.framework/Versions/A/Cocoa
    0x7fffffe00000 -     0x7fffffe01fff  libSystem.B.dylib ??? (???) <9AB4F1D1-89DC-0E8A-DC8E-A4FE4D69DB69> /usr/lib/libSystem.B.dylib

Model: MacBookPro7,1, BootROM MBP71.0039.B0B, 2 processors, Intel Core 2 Duo, 2.4 GHz, 4 GB, SMC 1.62f7
Graphics: NVIDIA GeForce 320M, NVIDIA GeForce 320M, PCI, 256 MB
Memory Module: global_name
AirPort: spairport_wireless_card_type_airport_extreme (0x14E4, 0x8D), Broadcom BCM43xx 1.0 (5.10.131.42.4)
Bluetooth: Version 2.4.5f3, 2 service, 12 devices, 1 incoming serial ports
Network Service: AirPort, AirPort, en1
Serial ATA Device: HL-DT-ST DVDRW  GS23N
USB Device: Built-in iSight, 0x05ac  (Apple Inc.), 0x8507, 0x24600000 / 2
USB Device: USB to ATA/ATAPI Bridge, 0x357d, 0x7788, 0x26400000 / 3
USB Device: Internal Memory Card Reader, 0x05ac  (Apple Inc.), 0x8403, 0x26100000 / 2
USB Device: BRCM2046 Hub, 0x0a5c  (Broadcom Corp.), 0x4500, 0x06600000 / 4
USB Device: Bluetooth USB Host Controller, 0x05ac  (Apple Inc.), 0x8213, 0x06610000 / 5
USB Device: IR Receiver, 0x05ac  (Apple Inc.), 0x8242, 0x06500000 / 3
USB Device: Apple Internal Keyboard / Trackpad, 0x05ac  (Apple Inc.), 0x0237, 0x06300000 / 2
----------- End crash report.

As far as I can tell, what is going on here is that OpenSSL wants to 
increase the refcount on those darn DH params (or maybe part thereof), 
seeks to acquire a lock on that refcount, and then crashes.

It's worth noticing openssl-1.1.1g/include/internal/refcount.h contains 
a number of implementations of the CRYPTO_UP_REF and CRYPTO_DOWN_REF 
operations, most of which don't seem to use the final lock parameter 
of these macros, but my compiler ends up using the very last definition, 
which calls various pthread_??? functions with that as argument, so 
someone forgetting to initialise that lock could handily explain what 
is going wrong here. 
Whether that error would be on the part of OpenSSL or TclTLS, however, 
I couldn't say. But all OpenSSL tests pass.

Segfault under wish at first tls::import, not under tclsh