libbpf: Properly build zip.o

The sync script does not seem to be automatically adding newly added
files added to the kernel repo build to the local Makefile. Do that now.

Signed-off-by: Daniel Müller <deso@posteo.net>

src/Makefile

@@ -52,7 +52,7 @@ STATIC_OBJDIR := $(OBJDIR)/staticobjs
 OBJS := bpf.o btf.o libbpf.o libbpf_errno.o netlink.o \
 	nlattr.o str_error.o libbpf_probes.o bpf_prog_linfo.o \
 	btf_dump.o hashmap.o ringbuf.o strset.o linker.o gen_loader.o \
-	relo_core.o usdt.o
+	relo_core.o usdt.o zip.o
 SHARED_OBJS := $(addprefix $(SHARED_OBJDIR)/,$(OBJS))
 STATIC_OBJS := $(addprefix $(STATIC_OBJDIR)/,$(OBJS))