bpftool: Allow add linker flags via EXTRA_LDFLAGS variable

Adding EXTRA_LDFLAGS allowing user to specify extra flags
for LD_FLAGS variable. Also adding LDFLAGS to build command
line.
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

@@ -49,6 +49,9 @@ CFLAGS += -DBPFTOOL_VERSION='"$(BPFTOOL_VERSION)"'
 ifneq ($(EXTRA_CFLAGS),)
 CFLAGS += $(EXTRA_CFLAGS)
 endif
+ifneq ($(EXTRA_LDFLAGS),)
+LDFLAGS += $(EXTRA_LDFLAGS)
+endif
 
 LIBS = -lelf -lbfd -lopcodes $(LIBBPF)
 
@@ -94,7 +97,7 @@ $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<
 
 $(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
-	$(QUIET_LINK)$(CC) $(CFLAGS) -o $@ $^ $(LIBS)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS)
 
 $(OUTPUT)%.o: %.c
 	$(QUIET_CC)$(COMPILE.c) -MMD -o $@ $<