Avoid qt keywords in installed headers

Change-Id: I14f3e02d2b568ae16beb07c8920df37981f3d0da
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 8e218c11c0dd3ab6baa66c151620a00fde24d898)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/kernel/qplatformwindow_p.h

@@ -112,7 +112,7 @@ public:
         auto role = std::any_cast<T *>(&anyRole);
         return role ? *role : nullptr;
     }
-signals:
+Q_SIGNALS:
     void surfaceCreated();
     void surfaceDestroyed();
     void xdgActivationTokenCreated(const QString &token);