Add missing header for atexit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182672 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ExecutionEngine/RTDyldMemoryManager.cpp b/lib/ExecutionEngine/RTDyldMemoryManager.cpp
index 0372bb6..6eee0d5 100644
--- a/lib/ExecutionEngine/RTDyldMemoryManager.cpp
+++ b/lib/ExecutionEngine/RTDyldMemoryManager.cpp
@@ -16,6 +16,8 @@
 #include "llvm/Support/DynamicLibrary.h"
 #include "llvm/Support/ErrorHandling.h"
 
+#include <cstdlib>
+
 #ifdef __linux__
   // These includes used by RTDyldMemoryManager::getPointerToNamedFunction()
   // for Glibc trickery. See comments in this function for more information.