How about this

Author: kbeckmann

sw/n64/testrom/Makefile

@@ -23,8 +23,10 @@ testrom.z64: N64_ROM_TITLE = "PicoCart64 Test ROM"
 
 $(BUILD_DIR)/testrom.elf: $(OBJS) | $(BUILD_DIR)
 
-$(BUILD_DIR):
-	mkdir -p $@
+$(BUILD_DIR)/testrom.o: $(BUILD_DIR)/git_info.h
+
+$(BUILD_DIR)/git_info.h:
+	mkdir -p $(BUILD_DIR)
 	echo -n "#define GIT_REV 0x" > $(BUILD_DIR)/git_info.h
 	git rev-parse --short=8 HEAD >> $(BUILD_DIR)/git_info.h
 .PHONY: $(BUILD_DIR)