tools lib bpf: Change FEATURE-DUMP to FEATURE-DUMP.libbpf

Commit ed63f34c02 ("perf tools: Make perf
depend on libbpf") triggers the build of libbpf when building the perf
tools, dynamically creating FEATURE-DUMP.libbpf.

It failed to update the tools/lib/bpf/.gitignore file to have that
prefix, fix it.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 65f041bee7 ("tools lib bpf: Use FEATURE_USER to allow building in the same dir as perf")
Link: http://lkml.kernel.org/r/1446706594-4142-1-git-send-email-yunlong.song@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/bpf/.gitignore

@@ -1,2 +1,2 @@
 libbpf_version.h
-FEATURE-DUMP
+FEATURE-DUMP.libbpf

tools/lib/bpf/Makefile

@@ -180,7 +180,7 @@ config-clean:
 clean:
 	$(call QUIET_CLEAN, libbpf) $(RM) *.o *~ $(TARGETS) *.a *.so $(VERSION_FILES) .*.d \
 		$(RM) LIBBPF-CFLAGS
-	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP
+	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf