bpftool: Allow to add compiler flags via EXTRA_CFLAGS variable

Adding EXTRA_CFLAGS allowing user to specify extra flags
for CFLAGS variable.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/Makefile

@@ -46,6 +46,10 @@ CFLAGS += -DPACKAGE='"bpftool"' -D__EXPORTED_HEADERS__ \
 	-I$(srctree)/tools/lib/bpf \
 	-I$(srctree)/tools/perf
 CFLAGS += -DBPFTOOL_VERSION='"$(BPFTOOL_VERSION)"'
+ifneq ($(EXTRA_CFLAGS),)
+CFLAGS += $(EXTRA_CFLAGS)
+endif
+
 LIBS = -lelf -lbfd -lopcodes $(LIBBPF)
 
 INSTALL ?= install