configure: the musl guard for PR_SET_VMA_ANON_NAME tests an unset variable #159885

gh-143730 disabled the PR_SET_VMA_ANON_NAME check on musl, but the guard tests a variable
that is never set:

configure.ac:6009:AS_IF([test "$ac_cv_libc" != musl], [

ac_cv_libc appears nowhere else, so the check always runs.

On x86_64 musl this goes unnoticed, because the conftest fails to compile anyway and the macro
stays undefined. On i686 musl it compiles, _Py_HAVE_PR_SET_VMA_ANON_NAME gets defined, and the
build then fails on the conflict the guard was meant to avoid:

In file included from ../Include/internal/pycore_mmap.h:16, from ../Objects/obmalloc.c:5:
/usr/include/sys/prctl.h:88:8: error: redefinition of 'struct prctl_mm_map'
/usr/include/linux/prctl.h:134:8: note: originally defined here

Workaround: ./configure ac_cv_have_decl_PR_SET_VMA_ANON_NAME=no.

3.14 is unaffected (no pycore_mmap.h).

Linked PRs

• gh-143632: Fix the musl check for PR_SET_VMA_ANON_NAME #159886