add header for 'memset'.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76837 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Allocator.cpp b/lib/Support/Allocator.cpp
index f5a2078..e302f0b 100644
--- a/lib/Support/Allocator.cpp
+++ b/lib/Support/Allocator.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Support/Recycler.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/Streams.h"
+#include <cstring>
 
 namespace llvm {