Fix corecrt_math_defines.h macro redefinition warnings with MSVC Qt 6 builds

app/app.pro

@@ -48,6 +48,9 @@ win32 {
 
     INCLUDEPATH += $$PWD/../libs/windows/include
     LIBS += ws2_32.lib winmm.lib dxva2.lib ole32.lib gdi32.lib user32.lib d3d9.lib dwmapi.lib dbghelp.lib
+
+    # Work around a conflict with math.h inclusion between SDL and Qt 6
+    DEFINES += _USE_MATH_DEFINES
 }
 macx {
     INCLUDEPATH += $$PWD/../libs/mac/include