Fix a build break with xray

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

Reviewers: dberris, bkramer

Reviewed By: dberris

Differential Revision: https://reviews.llvm.org/D30389

llvm-svn: 297794
diff --git a/compiler-rt/lib/xray/xray_utils.cc b/compiler-rt/lib/xray/xray_utils.cc
index 69e7b98..5d6390c 100644
--- a/compiler-rt/lib/xray/xray_utils.cc
+++ b/compiler-rt/lib/xray/xray_utils.cc
@@ -15,6 +15,7 @@
 #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>