Re #11422 Solve compatibility problem with Qwt versions<5.2.0

Code/Mantid/MantidPlot/src/plot2D/PowerScaleEngine.cpp

@@ -28,6 +28,7 @@
  ***************************************************************************/
 
 #include "PowerScaleEngine.h"
+#include "qwt_compat.h"
 
 /*!
   Return a dummy transformation

Code/Mantid/MantidPlot/src/plot2D/ScaleEngine.cpp

@@ -28,6 +28,7 @@
  ***************************************************************************/
 #include "ScaleEngine.h"
 #include "PowerScaleEngine.h"
+#include "qwt_compat.h"
 #include <limits.h>
 
 QwtScaleTransformation* ScaleEngine::transformation() const