[libc++][AIX] Use non-unique implementation for typeinfo comparison

Summary:
The AIX linker does not merge typeinfos when shared libraries are involved, which causes address comparison to fail although the types are the same. This patch changes to use the non-unique implementation for typeinfo comparison for AIX.

Reviewed by: hubert.reinterpretcast, philnik, libc++

Differential Revision: https://reviews.llvm.org/D130715