implement PR3177 - "__extension__ union" not supported in C++ mode

llvm-svn: 61180
diff --git a/clang/test/Parser/cxx-class.cpp b/clang/test/Parser/cxx-class.cpp
index 5afa8d6..39b787f 100644
--- a/clang/test/Parser/cxx-class.cpp
+++ b/clang/test/Parser/cxx-class.cpp
@@ -27,3 +27,12 @@
 {
   struct local {};
 }
+
+// PR3177
+typedef union {
+  __extension__ union {
+    int a;
+    float b;
+  } y;
+} bug3177;
+