Fix a build break with xray

[trixirt]

Summary

Building compiler-rt with clang 3.7 broken, could not find mkstemp

[dberris]

LGTM -- it's amazing though how long this has been there, and how we haven't got build-bots complaining about it.

[trixirt]

Can someone check this in ?

[dberris]

Thanks @trixirt -- I'll land this now.

compiler-rt/trunk/lib/xray/xray_utils.cc

 // This file is a part of XRay, a dynamic runtime instrumentation system.
 //
 //===----------------------------------------------------------------------===//
 #include "xray_utils.h"
 
 #include "sanitizer_common/sanitizer_common.h"
 #include "xray_defs.h"
 #include "xray_flags.h"
+#include <stdlib.h>
 #include <cstdio>
 #include <errno.h>
 #include <fcntl.h>
 #include <iterator>
 #include <sys/types.h>
 #include <tuple>
 #include <unistd.h>
 #include <utility>