add testcase we already handle.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@54967 91177308-0d34-0410-b5e6-96231b3b80d8

test/Sema/init.c

@@ -50,3 +50,7 @@ int pbool(void) {
   return pbool2;
 }
 
+
+// rdar://5870981
+union { float f; unsigned u; } u = { 1.0f };
+