C++11: add support for static_assert.

Change-Id: I82d8d60acaa9265fd25e0a3734855b19bdef9c06
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

tests/manual/plain-cplusplus/main.cpp

@@ -145,6 +145,7 @@ void parse(const char *fileName, const char *source, unsigned size)
     Control control;
     TranslationUnit unit(&control, control.stringLiteral(fileName));
     unit.setSource(source, size);
+    unit.setCxxOxEnabled(true);
     unit.parse();
 
 #if 1