[Bug libstdc++/92143] std::pmr::polymorphic_allocator<char> throws bad_alloc on macOS

[gcc-bugzilla at daryl dot haresign.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92143

--- Comment #4 from Daryl Haresign <gcc-bugzilla at daryl dot haresign.com> ---
As for conformance, the latest C draft says:

The aligned_alloc function allocates space for an object whose alignment is
specified by alignment, whose size is specified by size, and whose value is
indeterminate. If the value of alignment is not a valid alignment supported by
the implementation the function shall fail by returning a null pointer.

C11 said:

The aligned_alloc function allocates space for an object whose alignment is
specified by alignment, whose size is specified by size, and whose value is
indeterminate. The value of alignment shall be a valid alignment supported by
the implementation and the value of size shall be an integral multiple of
alignment.

So it seems macOS and AIX's implementations are technically conformant. 
Perhaps GCC should determine whether the platform supports alignments less than
sizeof(void*) when GCC is built, and put a new macro in c++config.h (assuming
that's how that file is constructed)?