I think there was a discussion about this and we concluded that it was getting ugly so this second approach on top was followed. Perhaps a better approach to using#undef and all this stuff on top is to create a macro to replace the following where needed:

#ifdef_PC_ALLOC_SIZE_MINreturn_PC_ALLOC_SIZE_MIN;#elsereturn0;#endif

You know, when macros get bad make another :-)

Ok, I'll take care of this in different way.

But I'd like to finish CI for BSD platform before I move.

@catap

re:Let me ping @LeeTibbert as well.

I have been offline for awhile and am about to go offline for another longish (weeks) while.
I'll take a look if I can before I go offline again.

My rapid "wet" reading is that section probably long predates me and has to do with
what is and is_not POSIX and what is intended to be allowed in SN posixlib.

I believe, but would have to re-ground myself, that XOPEN is a superset of POSIX and
that the original intent was that only POSIX and possibly XSI were allowed in posixlib.

Compiling with _XOPEN_VERSION macro defined enabled the compilation of "intended-to-be-excluded"
XOPEN functions, so it was #undef'd. I think the #undef was because we do not have absolute control
over the compiler flags passed in; a user could -D_XOPEN_VERSION.

TL;DR - in case events need action before I can do all my evidence collection & tracing.

I think the ugly but cleanest solution is to put explicit OS specific guards around the _XOPEN_VERSION
handling. Again, ugly but gives future devos a sporting chance of understanding the logic chain.

That is, have the existing section for linux, MacOS (Windows?) and a new section
which does the alternate define of this PR for FreeBSD, NetBSD, and known others as they
may apply.

I would end with a "Unsupported OS" #error pragma.

Each OS gets what they are happy with and what has been tested & shown to work.