perf tools: Make sure fixdep is built before libbpf

While doing 'make -C tools/perf build-test':

   LD       fixdep-in.o
   LINK     fixdep
 /bin/sh: /home/acme/git/linux/tools/build/fixdep: Permission denied
 make[6]: *** [bpf.o] Error 1
 make[5]: *** [libbpf-in.o] Error 2
 make[4]: *** [/home/acme/git/linux/tools/lib/bpf/libbpf.a] Error 2
 make[4]: *** Waiting for unfinished jobs....

The fixdep tool needs to be built as the first binary.  Libraries are
built in paralel, so each of them needs to depend on fixdep target.
Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20151028204450.GA25553@krava.redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -430,7 +430,7 @@ $(LIBAPI)-clean:
 	$(call QUIET_CLEAN, libapi)
 	$(Q)$(MAKE) -C $(LIB_DIR) O=$(OUTPUT) clean >/dev/null
 
-$(LIBBPF): FORCE
+$(LIBBPF): fixdep FORCE
 	$(Q)$(MAKE) -C $(BPF_DIR) O=$(OUTPUT) $(OUTPUT)libbpf.a
 
 $(LIBBPF)-clean: