Bug 740452 - Move check-sync-dirs test to a named target so it can be run independent of configure. r=ted

client.mk

@@ -368,8 +368,7 @@ endif
 ####################################
 # Build it
 
-realbuild::  $(OBJDIR)/Makefile $(OBJDIR)/config.status
-	@$(PYTHON) $(TOPSRCDIR)/js/src/config/check-sync-dirs.py $(TOPSRCDIR)/js/src/config $(TOPSRCDIR)/config
+realbuild::  $(OBJDIR)/Makefile $(OBJDIR)/config.status check-sync-dirs-config
 	$(MOZ_MAKE)
 
 ####################################
@@ -427,6 +426,12 @@ cleansrcdir:
 	   build/autoconf/clean-config.sh; \
 	fi;
 
+## Sanity check $X and js/src/$X are in sync
+.PHONY: check-sync-dirs
+check-sync-dirs: check-sync-dirs-build check-sync-dirs-config
+check-sync-dirs-%:
+	@$(PYTHON) $(TOPSRCDIR)/js/src/config/check-sync-dirs.py $(TOPSRCDIR)/js/src/$* $(TOPSRCDIR)/$*
+
 echo-variable-%:
 	@echo $($*)