hw/xwin: Clarify an if statement mixed with ifdef in winSetEngine()

Use the same pattern as elsewhere so it's a bit clearer what we
are checking

Signed-off-by: Ryan Pavlik <rpavlik@iastate.edu>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>
Reviewed-by: Jon TURNEY <jon.turney@dronecode.org.uk>

hw/xwin/winengine.c

@@ -192,15 +192,12 @@ winSetEngine (ScreenPtr pScreen)
 
   /* ShadowGDI is the only engine that supports Multi Window Mode */
   if (
-#ifdef XWIN_MULTIWINDOWEXTWM
-      pScreenInfo->fMWExtWM
-#else
       FALSE
+#ifdef XWIN_MULTIWINDOWEXTWM
+      || pScreenInfo->fMWExtWM
 #endif
 #ifdef XWIN_MULTIWINDOW
       || pScreenInfo->fMultiWindow
-#else
-      || FALSE
 #endif
       )
     {