Fix SDL plugin building on PPC64le

SDL.h redefines bool, which breaks the build.

Task-number: QTBUG-60679
Change-Id: I1ae833b26e867c0127000d8b09eb53fe8cdac0b8
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/plugins/gamepads/sdl2/qsdlgamepadbackend.cpp

@@ -38,6 +38,8 @@
 #include <QtCore/QDebug>
 
 #include <SDL.h>
+// Reset bool redefinition from SDL header
+#undef bool
 
 QT_BEGIN_NAMESPACE