Fix detection of Hdr:Wimp being included before Hdr:Services

Detail:
  The trick used only works with variable name symbols; other symbols remain
  defined after the end of the first pass of assembly
Admin:
  Should enable us to track down components that will need changing from
  examination of the build logs

hdr/Wimp

@@ -148,8 +148,8 @@ Service_ErrorStarting           #       1
 Service_ErrorButtonPressed      #       1
 Service_ErrorEnding             #       1
   ]
-                                ^       WimpService+3
-Service_WimpToolSpritesChanged  #       1
+                                GBLA    Service_WimpToolSpritesChanged
+Service_WimpToolSpritesChanged  SETA    WimpService+3
 
 ; ReadSysInfo reason codes
                                 ^       0