Bug 492326 Make symbol nspr_use_zone_allocator to be global r=bsmedberg

toolkit/xre/nsAppRunner.cpp

@@ -2591,7 +2591,7 @@ static void MOZ_gdk_display_close(GdkDisplay *display)
  * By defining the symbol here, we can avoid the wasted lookup and hopefully
  * improve startup performance.
  */
-PRBool nspr_use_zone_allocator = PR_FALSE;
+NS_VISIBILITY_DEFAULT PRBool nspr_use_zone_allocator = PR_FALSE;
 
 #ifdef MOZ_SPLASHSCREEN
 #define MOZ_SPLASHSCREEN_UPDATE(_i)  do { if (splashScreen) splashScreen->Update(_i); } while(0)