[libc++] [test] ASSERT_WITH_LIBRARY_INTERNAL_ALLOCATIONS is not supported on AIX.

I believe all four of these failures are directly due to the pattern where
allocations in the dylib are unobserved by the client program. If AIX32 and AIX64
don't support that, we should just disable the ASSERT_WITH_LIBRARY_INTERNAL_ALLOCATIONS
macro on AIX, and then we don't need to XFAIL these tests.

This also means I won't need to XFAIL a dozen other tests in D89057,
which rely heavily on ASSERT_WITH_LIBRARY_INTERNAL_ALLOCATIONS and
also currently fail on AIX.
See https://buildkite.com/llvm-project/libcxx-ci/builds/7669

Differential Revision: https://reviews.llvm.org/D116866