perf tools: Use __weak definition from linux/compiler.h

Replace __attribute__((weak)) with __weak definition

Signed-off-by: Rui Teng <rui.teng@linux.vnet.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1469671557-2256-2-git-send-email-rui.teng@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -828,8 +828,7 @@ static int write_group_desc(int fd, struct perf_header *h __maybe_unused,
  * default get_cpuid(): nothing gets recorded
  * actual implementation must be in arch/$(ARCH)/util/header.c
  */
-int __attribute__ ((weak)) get_cpuid(char *buffer __maybe_unused,
-				     size_t sz __maybe_unused)
+int __weak get_cpuid(char *buffer __maybe_unused, size_t sz __maybe_unused)
 {
 	return -1;
 }