Merge pull request #8915 from eeckstein/disable-md-test

disabled flaky test

Author: eeckstein

unittests/runtime/Metadata.cpp

@@ -389,6 +389,8 @@ ProtocolDescriptor ProtocolNoWitnessTable{
     .withDispatchStrategy(ProtocolDispatchStrategy::ObjC)
 };
 
+#if 0 // disabled because of rdar://problem/31759879
+
 TEST(MetadataTest, getExistentialMetadata) {
   const ProtocolDescriptor *protoList1[] = {};
   RaceTest_ExpectEqual<const ExistentialTypeMetadata *>(
@@ -586,6 +588,8 @@ TEST(MetadataTest, getExistentialMetadata) {
     });
 }
 
+#endif
+
 static SWIFT_CC(swift) void destroySuperclass(SWIFT_CONTEXT HeapObject *toDestroy) {}
 
 struct {