[NFC][tests][AIX] XFAIL test for lack of visibility support

With the addition of `__attribute__((visibility("hidden")))` to the test, the test fails because AIX's current default behaviour is to ignore hidden visibility, so the expected error is not seen. This patch marks the test `XFAIL` on AIX for now.

Reviewed By: cebowleratibm

Differential Revision: https://reviews.llvm.org/D122519