Make the makefile work more than once

Author: geofft

kernel-cflags-finder/Makefile

@@ -5,6 +5,8 @@ clean-files := dummy.c
 $(M)/dummy.c:
 	@echo $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(__c_flags) $(modkern_cflags)
 	@touch $@
+
+.PHONY: $(M)/dummy.c
 else
 KDIR ?= /lib/modules/$(shell uname -r)/build
 CLANG ?= clang