[clang][DebugInfo] Disable objective-C tests on AIX and z/OS (#154951)

These tests don't work due to limitations in backend support, so it's
better to mark them uniformly unsupported on AIX and z/OS.

Author: daltenty

clang/test/DebugInfo/ObjC/lit.local.cfg

@@ -0,0 +1,5 @@
+# objective-C is not supported on AIX and zOS
+unsupported_platforms = [ "system-aix", "system-zos" ]
+
+if any(up in config.available_features for up in unsupported_platforms):
+    config.unsupported = True