These test cases are testing features not available when either
targeting the s390x-ibm-zos target or use tools/features not available
on the z/OS operating system. In a couple cases the lit test had a
number of subtests with one or two that aren't supported on z/OS. Rather
than mark the entire test as unsupported I split out the unsupported
tests into a separate test case.
Merge definition visibility the same way we do for other decls. Without
the fix the added test emits `-Wobjc-method-access` as it cannot find a
visible protocol. Make this warning `-Werror` so the test would fail
when protocol visibility regresses.
rdar://83600696
Differential Revision: https://reviews.llvm.org/D111860
