perf diff: Add missing handler for PERF_RECORD_MMAP2 events

Without mmap2, perf diff fails to find the symbol name. The default
symbol sort key doesn't work well.
Signed-off-by: Kan Liang <kan.liang@intel.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1416328700-1836-2-git-send-email-kan.liang@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-diff.c

@@ -357,6 +357,7 @@ static int diff__process_sample_event(struct perf_tool *tool __maybe_unused,
 static struct perf_tool tool = {
 	.sample	= diff__process_sample_event,
 	.mmap	= perf_event__process_mmap,
+	.mmap2	= perf_event__process_mmap2,
 	.comm	= perf_event__process_comm,
 	.exit	= perf_event__process_exit,
 	.fork	= perf_event__process_fork,