Fix test failure from r362435

Apparently I forgot to do an open brace in a namespace, so we get an
error about an extra closing brace.

llvm-svn: 362443

clang/test/SemaCXX/nothrow-vs-exception-specs.cpp

@@ -89,7 +89,7 @@ public:
 };
 }
 
-namespace FuncPointerReferenceConverts
+namespace FuncPointerReferenceConverts {
 void FuncToBeRefed();
 
 #ifndef CPP17