Running os-test on glibc's POSIX headers

[Jonas 'Sortie' Termansen]

Oh it's wonderful to hear my POSIX.1-2024 blog post was useful! The
new os-test include suite is an evolution of that concept since I was
able to generate exact machine definitions of what's new, and even
diff old and new POSIX.

I just made a namespace pollution checker and published data for every
system:

https://sortix.org/os-test/namespace/

glibc scores very highly with a top score of 84% and is careful to
avoid namespace pollution, but fails to remove obsolete declarations
that no longer exist in POSIX.1-2024, and also has some sys/socket.h
reserved namespace issues (it turns out AF_* and a few others are only
reserved in XSI for some reason).

os-test respects CC, CFLAGS, CPPFLAGS, LDFLAGS (-lc -lpthread -lm
-lrt -lxnet only), and EXTRA_LDFLAGS (any other lib, see README). It
should be trivial to run glibc against a development glibc build using
the standard methods. Cross-compilation is also supported. If there's
anything I do to to make os-test more useful or easy to use, please
let me know. It's designed to run everywhere and be useful for
everyone :)

If anyone uses this data to make improvements, I would love to hear
about it :D