Fix wxMSW build with wxUSE_UXTHEME=0

Include wx/msw/uxtheme.h even when wxUSE_UXTHEME == 0 because
wxUxThemeEngine::GetIfActive() and MARGINS struct are still used even then in
anybutton.cpp and menuitem.cpp respectively.

src/msw/menuitem.cpp

@@ -47,10 +47,7 @@
 
 #include "wx/msw/private.h"
 #include "wx/msw/dc.h"
-
-#if wxUSE_UXTHEME
-    #include "wx/msw/uxtheme.h"
-#endif
+#include "wx/msw/uxtheme.h"
 
 // ---------------------------------------------------------------------------
 // macro