SafeStack: Add another missing header to try to fix FreeBSD build.

llvm-svn: 240564
diff --git a/compiler-rt/lib/safestack/safestack.cc b/compiler-rt/lib/safestack/safestack.cc
index 0e52c2a..504bd3c 100644
--- a/compiler-rt/lib/safestack/safestack.cc
+++ b/compiler-rt/lib/safestack/safestack.cc
@@ -19,6 +19,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <sys/resource.h>
+#include <sys/types.h>
 #include <sys/user.h>
 
 #include "interception/interception.h"