Fixes for wxQt build under Cygwin

Include the missing headers, notable QtGui/QFont from wx/fontutil.h which uses
a QFont object.

Closes #16750.

src/qt/colour.cpp

@@ -9,12 +9,18 @@
 
 // For compilers that support precompilation, includes "wx.h".
 #include "wx/wxprec.h"
-#include "wx/qt/private/utils.h"
 
 #ifdef __BORLANDC__
-#pragma hdrstop
+    #pragma hdrstop
 #endif
 
+#ifndef WX_PRECOMP
+    #include "wx/colour.h"
+#endif // WX_PRECOMP
+
+#include "wx/qt/private/utils.h"
+
+
 int wxColour::GetPixel() const
 {
     wxMISSING_IMPLEMENTATION( "wxColour::GetPixel" );