fix build on Arch Linux

qtimageformats/src/plugins/imageformats/jp2/qjp2handler.cpp:844:41:
error: no declaration of «pow»
  844 |     const double jasperRate = minRate + pow((double(quality) / double(maxQuality)), 2) * maxRate;

Pick-to: 5.15
Change-Id: I085996c2db2251903b2a3e52e6e648831637c8f9
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/plugins/imageformats/jp2/qjp2handler.cpp

@@ -45,6 +45,7 @@
 #include "qcolor.h"
 
 #include <jasper/jasper.h>
+#include <math.h> // for pow
 
 QT_BEGIN_NAMESPACE