autoconf uses CFLAGS at configure time when performing many checks.  However,
tcl.m4 adds the strings <code>${CFLAGS_DEFAULT}</code> and
<code>${CFLAGS_WARNING}</code>.  Because of this, any autoconf test that passes
CFLAGS to the compiler at runtime fails.  One example is
<code>AC_TYPE_OFF_T</code>.  On a Linux system this test currently fails, and
autoconf erroneously configures the build as if there was no such type
available.  In one extension this leads to the error,

    <code>&lt;command-line&gt;: error: two or more data types in declaration specifiers</code>