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Re: toolchain/53314: strncasecmp conflict when cross-compiling libgroff on FreeBSD

The problem is not with FreeBSD's headers.  Doubtless there are bugs
in FreeBSD's headers, but in this case, the logic in our tree is doing
something wrong and we can straightforwardly fix it in our tree.

The problem in our tree is that there was a bodgy autoconf feature
that got baked into the groff configure script to attempt to _guess_
the correct declaration of the exit function by enumerating several
options, none of which is the one that FreeBSD uses now.

Because the autoconf-generated configure script fails to find the
declaration of exit, it gets confused and generates the wrong test
programs, leading it to infer that the system's strncasecmp
declaration is missing too.  On the basis of that, groff decides to
fantasize its own strncasecmp declaration, which, incidentally, also
disagrees with the standard one.

The bodgy autoconf feature was a combination of a workaround for a bug
dating back to 1988 in SunOS and difficulty with finding a usable
declaration for exit when the C++ compiler is being abused as a C
compiler[1].  Fortunately, this autoconf feature was removed in
2006[2], 12 years ago, when the bug it worked around was only 18 years

There are two obvious ways to fix this:

1. Patch the groff configure script to try an exit declaration that
   FreeBSD actually uses:

diff --git a/external/gpl2/groff/dist/configure b/external/gpl2/groff/dist/configure
index 107aadcae070..972b95703f29 100755
--- a/external/gpl2/groff/dist/configure
+++ b/external/gpl2/groff/dist/configure
@@ -2511,6 +2511,8 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
    'extern "C" void exit (int);' \
+   'extern "C" [[noreturn]] void exit (int);' \
+   'extern "C" _Noreturn void exit (int);' \
    'void exit (int);'
   cat >conftest.$ac_ext <<_ACEOF

2. Regenerate the groff configure script with a modern autoconf that
   doesn't twist itsef into knots trying to guess how to declare exit.

Neither of these requires changing FreeBSD; it is a legitimate bug in
NetBSD that the toolchain doesn't build on FreeBSD right now, and
rather embarrassing that it has been the case for months.


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