util/archive: Clean up Makefile

- Add warnings
- Enable warnings as errors:
- Add distclean target
- Add help target

BUG=None
TEST=make help; make all; make all WERROR=""

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: I1ae8a837003491f3ab123b3761e220556258e0c5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50652
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/archive/Makefile

@@ -1,14 +1,24 @@
 PROGRAM = archive
 HOSTCC ?= gcc
+WERROR=-Werror
+CFLAGS=-O2 -Wall -Wextra -Wshadow ${WERROR}
 
 SRCS = $(PROGRAM).c
 
 all: $(PROGRAM)
 
 $(PROGRAM): $(SRCS)
-	$(HOSTCC) -o $@ $^
+	$(HOSTCC) $(CFLAGS) -o $@ $^
 
 clean:
 	rm -f $(PROGRAM) *.o
 
-.PHONY: all clean
+distclean: clean
+
+help:
+	@echo "${PROGRAM}: Concatenate files and create an archive"
+	@echo "Targets: all, clean, distclean, help"
+	@echo "To disable warnings as errors, run make as:"
+	@echo "  make all WERROR=\"\""
+
+.PHONY: all clean distclean help