Clang: Forward compiler options for gcc/clang

Rely on clang to do the "right thing" with them.

Change-Id: I44adf2cd5c61549896da3fc9b7c35c2fb0142060
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/cpptools/projectpart.h

@@ -120,6 +120,7 @@ public:
 
     // Misc
     QStringList extraCodeModelFlags;
+    QStringList compilerFlags;
 };
 
 } // namespace CppTools