Switching on NU_CACHE by default. Use set NO_NU_CACHE=1 to switch it off.

config/config.mak

@@ -201,6 +201,11 @@ CFLAGS = $(CFLAGS) -FR
 CFLAGS=$(CFLAGS) -DSTANDALONE_IMAGE_LIB
 !endif
 
+!ifndef NO_NU_CACHE
+NU_CACHE = 1
+CFLAGS=$(CFLAGS) -DNU_CACHE
+!endif
+
 # Crash-reporting system.  http://www.fullcirclesoftware.com
 !ifdef MOZ_FULLCIRCLE
 CFLAGS=$(CFLAGS) -DMOZ_FULLCIRCLE