`posixmodule.c` doesn't detect xattr support on Linux with non-glibc (e.g. musl)

[thesamesam]

Bug report

posixmodule.c detects xattr support by checking for __GLIBC__ (and some other conditions) at

cpython/Modules/posixmodule.c

Line 277 in 86ebd5c

#if defined(HAVE_SYS_XATTR_H) && defined(__GLIBC__) && !defined(__FreeBSD_kernel__) && !defined(__GNU__)

. This incorrectly excludes the musl libc,which supports xattr functionality.

On a musl system, it's easy to reproduce with:

>>> import os
>>> os.listxattr 
Traceback (most recent call last): 
	File "", line 1, in
AttributeError: module 'os' has no attribute 'listxattr'

Your environment

• CPython versions tested on: 3.10.10/3.11.2/3.12.0_alpha5
• Operating system and architecture: Gentoo Linux, amd64, musl libc (not glibc)
• Downstream report in Gentoo: https://bugs.gentoo.org/894130
• Report in a Python-using project: AttributeError: module 'os' has no attribute 'listxattr' GNS3/gns3-gui#1392

Linked PRs

• gh-101857: Allow xattr detection on musl libc #101858
• [3.11] gh-101857: Allow xattr detection on musl libc (GH-101858) #101894