C++: Parse emit/Q_EMIT properly

The parser now understands emit/Q_EMIT as an expression statement.

Also, the recent fixes in the preprocessor introduced a side-effect
in the hanlding of code such as: emit signal(); Member signal started
being treated as a local use (parsed as a declaration) and possibily
being highlighted as unused variable.

Previously that worked by accident since there was an inconsistency
in the preprocessor on which only object-like macros were being
expanded even when the "no expand" flag was set. Then, the code
mentioned above was being parsed as an expression, what kind of worked.

Change-Id: I47a68ed4c1c1702872620b8ed7c7264fb0997034
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

src/libs/cplusplus/pp-engine.cpp

@@ -1813,6 +1813,10 @@ bool Preprocessor::isQtReservedWord(const ByteArrayRef &macroId)
         return true;
     else if (size == 5 && macroId.at(0) == 's' && macroId == "slots")
         return true;
+    else if (size == 4 && macroId.at(0) == 'e' && macroId == "emit")
+        return true;
+    else if (size == 6 && macroId.at(0) == 'Q' && macroId == "Q_EMIT")
+        return true;
     return false;
 }