Android.mk 推断文件是否存在，若存在则复制该文件到某个文件夹

$(shell test -f [文件] && echo yes)的值假设是yes, 则文件存在，然后进行shell cp 动作

HAVE_TEST_CUST_FILE := $(shell test -f vendor/huaqin/resource/$(HQ_PROJECT)_$(HQ_CLIENT)/$(LOCAL_PATH)/DroidSansFallback.ttf && echo yes)
ifeq ($(HAVE_TEST_CUST_FILE),yes)
$(shell cp -f vendor/huaqin/resource/$(HQ_PROJECT)_$(HQ_CLIENT)/$(LOCAL_PATH)/DroidSansFallback.ttf $(PRODUCT_OUT)/system/fonts/DroidSansFallback.ttf)
endif