[AIX][XCOFF] error on emit symbol visibility for XCOFF object file

This is a follow on to the revert of D84265 to add an error if we'd need
to write a non-zero visibility type in the xcoff object file. We can't
currently do that because we lack the auxilary header to interpret the
bits in XCOFF32. This is important because visibility is being enabled
in the assembly writing path, and without this error the visibility
could be silently ignored.

Differential Revision: https://reviews.llvm.org/D124392