perf header: Add is_perf_magic() func

With this function, other modules can basically check whether a file is
a legal perf data file by checking its first 8 bytes against all
possible perf magic numbers.

Change the function name from check_perf_magic to more meaningful
is_perf_magic as suggested by acme.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1351569369-26732-7-git-send-email-feng.tang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
index 879d215..5f1cd68 100644
--- a/tools/perf/util/header.h
+++ b/tools/perf/util/header.h
@@ -154,6 +154,7 @@
 int perf_event__process_build_id(struct perf_tool *tool,
 				 union perf_event *event,
 				 struct perf_session *session);
+bool is_perf_magic(u64 magic);
 
 /*
  * arch specific callback