Allow static_assert inside an anonymous union; fixes PR20021 as well as implements C++ Issue 1940.

llvm-svn: 211606
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index bdc8609..90499d2 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3754,6 +3754,8 @@
         }
       } else if (isa<AccessSpecDecl>(Mem)) {
         // Any access specifier is fine.
+      } else if (isa<StaticAssertDecl>(Mem)) {
+        // In C++1z, static_assert declarations are also fine.
       } else {
         // We have something that isn't a non-static data
         // member. Complain about it.