ClangTools: Show also diagnostics from project's header files

Fixes: QTCREATORBUG-21452
Change-Id: I73c85224e142f4f1d08c9ada75fe8359ebf0f984
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/clangtools/clangtoolsdiagnostic.h

@@ -66,6 +66,8 @@ public:
     bool hasFixits = false;
 };
 
+quint32 qHash(const Diagnostic &diagnostic);
+
 } // namespace Internal
 } // namespace ClangTools