Makefile: add libbpf dependency for XDP_TARGETS

Since commit a339ed6 the bpf_helpers.h files comes from libbpf.
Thus, add a Makefile build dependency for XDP_TARGETS.

This solved a build issue, where I didn't have any USER_TARGETS
in the directorys Makefile.

Fixes: a339ed6 ("Update libbpf to latest upstream version")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

Author: netoptimizer

common/common.mk

@@ -107,7 +107,7 @@ $(USER_TARGETS): %: %.c  $(OBJECT_LIBBPF) Makefile $(COMMON_MK) $(COMMON_OBJS) $
 	$(CC) -Wall $(CFLAGS) $(LDFLAGS) -o $@ $(COMMON_OBJS) \
 	 $< $(LIBS)
 
-$(XDP_OBJ): %.o: %.c  Makefile $(COMMON_MK) $(KERN_USER_H) $(EXTRA_DEPS)
+$(XDP_OBJ): %.o: %.c  Makefile $(COMMON_MK) $(KERN_USER_H) $(EXTRA_DEPS) $(OBJECT_LIBBPF)
 	$(CLANG) -S \
 	    -target bpf \
 	    -D __BPF_TRACING__ \