[mac/arm] Fix rtti codegen tests when running on an arm mac

shouldRTTIBeUnique() returns false for iOS64CXXABI, which causes
RTTI objects to be emitted hidden. Update two tests that didn't
expect this to happen for the default triple.

Also rename iOS64CXXABI to AppleARM64CXXABI, since it's used for
arm64-apple-macos triples too.

Part of PR46644.

Differential Revision: https://reviews.llvm.org/D91904