Makefile hard coded to use clang

[micolous]

The Makefiles for caption-inspector appear to be all hard coded to use clang:

caption-inspector/src/Makefile

Lines 137 to 143 in 476326f

	${CI_EXECUTABLE}: $(OBJS_WITH_PATH) main.o
	@echo "\n*** Compiling Caption Inpsector Executible. ***"
	clang -o ${CI_EXECUTABLE} ../obj/main.o $(OBJS_IN_OBJ_DIR) $(LD_FLAGS) $(LD_FLAGS_FFMPEG)
	no_ffmpeg: $(OBJS_WITH_PATH) main.o
	@echo "\n*** Compiling Caption Inpsector Executible without FFMPEG. ***"
	clang -o ${CI_EXECUTABLE} ../obj/main.o $(OBJS_IN_OBJ_DIR) $(LD_FLAGS)

This project builds fine on gcc 9.3 too.

One can use the implicit variable $(CC) to get whatever the user-preferred compiler (and its location) is. It also makes it easier to set up a CI build matrix with other compilers.