[libc++] allow redefined macro in non_trivial_copy_move_ABI test

__config defines _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
on FreeBSD, which conflicts with a command-line definition used by the
non_trivial_copy_move_ABI test.

Add -Wno-macro-redefined to ADDITIONAL_COMPILE_FLAGS in this test.

Reviewed By: philnik

Differential Revision: https://reviews.llvm.org/D141774