tools/bpftool: Add -Wall when building BPF programs

No additional warnings are generated by enabling this, but having it
enabled will help avoid regressions.

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210113223609.3358812-2-irogers@google.com

tools/bpf/bpftool/Makefile

@@ -166,7 +166,7 @@ $(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h $(LIBBPF)
 		-I$(srctree)/tools/include/uapi/ \
 		-I$(LIBBPF_PATH) \
 		-I$(srctree)/tools/lib \
-		-g -O2 -target bpf -c $< -o $@ && $(LLVM_STRIP) -g $@
+		-g -O2 -Wall -target bpf -c $< -o $@ && $(LLVM_STRIP) -g $@
 
 $(OUTPUT)%.skel.h: $(OUTPUT)%.bpf.o $(BPFTOOL_BOOTSTRAP)
 	$(QUIET_GEN)$(BPFTOOL_BOOTSTRAP) gen skeleton $< > $@