add zwc make target

Makefile

@@ -5,3 +5,7 @@ all:
 pkg:
 	$(MAKE) -C gitstatus pkg
 	$(or $(ZSH),:) -fc 'for f in *.zsh-theme internal/*.zsh; do zcompile -R -- $$f.zwc $$f || exit; done'
+
+zwc:
+	$(MAKE) -C gitstatus zwc
+	$(or $(ZSH),:) -fc 'for f in *.zsh-theme internal/*.zsh; do zcompile -R -- $$f.zwc $$f || exit; done'