build: undefine debug helper templates used by subdir.mk if the DEBUG variable is empty, speeds up "make prereq" by 25% when lots of packages are installed

SVN-Revision: 26434

include/debug.mk

@@ -21,6 +21,8 @@ ifeq ($(DUMP),)
   endif
 endif
 
+ifneq ($(DEBUG),)
+
 define debug
 $$(findstring $(2),$$(if $$(DEBUG_SCOPE_DIR),$$(if $$(filter $$(DEBUG_SCOPE_DIR)%,$(1)),$(build_debug)),$(build_debug)))
 endef
@@ -38,4 +40,12 @@ $(call warn,$(1),$(2),$(3)	$(4))
 $(4)
 endef
 
+else
+
+debug:=
+warn:=
+debug_eval:=
+warn_eval = $(4)
+
+endif