Need to check availability before use of macros. (#3254)

* Need to check availability before use of macros.

* Get rid of PCH and enforce macro definition.

* Remove prefix

* Switch to global warning instead, much better.

Source/ASImageNode+AnimatedImage.mm

@@ -24,6 +24,7 @@
 #import <AsyncDisplayKit/ASNetworkImageNode.h>
 #import <AsyncDisplayKit/ASWeakProxy.h>
 
+#define ASAnimatedImageDebug  0
 
 @interface ASNetworkImageNode (Private)
 - (void)_locked_setDefaultImage:(UIImage *)image;