Utils: Fix build on Windows

Partially reverts 9508ee134.

Change-Id: I5b6f865a4b404ce8e510bc678ec1ce84ccb9e013
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/libs/utils/minimizableinfobars.h

@@ -28,6 +28,7 @@
 #include "utils_global.h"
 
 #include "id.h"
+#include "infobar.h"
 
 #include <QHash>
 #include <QObject>
@@ -40,9 +41,6 @@ QT_END_NAMESPACE
 
 namespace Utils {
 
-class InfoBar;
-class InfoBarEntry;
-
 class QTCREATOR_UTILS_EXPORT MinimizableInfoBars : public QObject
 {
     Q_OBJECT