gh-90548: Fix musl version detection with --strip-all

[cdce8p]

The change introduced in #131313 accidentally broke the musl version detection for test.support.linked_with_musl if cpython is compiled with --strip-all. In these cases the regex in platform.libc_ver should match the filename: libc.musl-x86_64.so.1.
https://pkgs.alpinelinux.org/contents?file=libc.*&path=&name=musl&branch=edge&repo=main&arch=

--strip-all is used among other things by the Alpine based Python docker image.
https://github.com/docker-library/python/blob/19c93d12094b07ecc21f67144a309c2fa0a10ef0/3.14-rc/alpine3.22/Dockerfile#L74

With this change:

./configure
make LDFLAGS="-Wl,--strip-all"

/usr/src # LD_LIBRARY_PATH=$PWD ./python.exe
Python 3.14.0rc2 (main, Aug 16 2025, 14:50:44) [GCC 14.2.0] on linux
>>> import test.support
>>> test.support.linked_to_musl()
(1,)

/usr/src # LD_LIBRARY_PATH=$PWD ./python.exe -m test.pythoninfo|grep libc
platform.libc_ver: musl 1

/CC @bitdancer

• Issue: Multiple test failures on Alpine 3.15 / musl-1.2.2-r7 #90548

[AA-Turner]

The added pattern seems ostensibly reasonable.

[cdce8p]

@AA-Turner I believe the OS-Linux label might be incorrect. Alpine is technically unsupported. Never the less, since #131313 was added in 3.14, I would still appreciate if it could be backported. Especially as it also indirectly fixes test.support.linked_with_musl and thus some of the test failures on Alpine linux.

[AA-Turner]

I would still appreciate if it could be backported.

I already added the backport label. Anything else missing?

I believe the OS-Linux label might be incorrect. Alpine is technically unsupported.

Fair enough, though "linux" is sufficiently vague that I think it is probably fine. Ideally we'd have a "libc-musl" label, but given as you say Alpine is unsupported, it's too niche at present.

[cdce8p]

I would still appreciate if it could be backported.

I already added the backport label. Anything else missing?

No, all good. I just wasn't sure if a fix for an unsupported platform meant it couldn't be backported.

[StanFromIreland]

Fair enough, though "linux" is sufficiently vague that I think it is probably fine. Ideally we'd have a "libc-musl" label, but given as you say Alpine is unsupported, it's too niche at present.

FWIW we have a "musl" section in the Unsupported platforms project.

[cdce8p]

@vstinner Would you mind taking a look at this one? I believe you also reviewed the predecessor #131313.

[vstinner]

LGTM

[miss-islington-app]

Thanks @cdce8p for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-138348 is a backport of this pull request to the 3.14 branch.

[vstinner]

Merged, thanks for the fix and added tests!