Add test case for __has_feature(objc_weak_class).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102639 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Preprocessor/non_fragile_feature.m b/test/Preprocessor/non_fragile_feature.m
index 552209d..1f67ed3 100644
--- a/test/Preprocessor/non_fragile_feature.m
+++ b/test/Preprocessor/non_fragile_feature.m
@@ -6,3 +6,7 @@
 #if !__has_feature(objc_nonfragile_abi)
 #error Non-fragile ABI used for compilation but feature macro not set.
 #endif
+
+#if !__has_feature(objc_weak_class)
+#error objc_weak_class should be enabled with nonfragile abi
+#endif