Add <cstddef> for use of std::ptrdiff_t.

llvm-svn: 203086
diff --git a/llvm/lib/Support/StreamableMemoryObject.cpp b/llvm/lib/Support/StreamableMemoryObject.cpp
index df7620a..d7804e6 100644
--- a/llvm/lib/Support/StreamableMemoryObject.cpp
+++ b/llvm/lib/Support/StreamableMemoryObject.cpp
@@ -10,6 +10,7 @@
 #include "llvm/Support/StreamableMemoryObject.h"
 #include "llvm/Support/Compiler.h"
 #include <cassert>
+#include <cstddef>
 #include <cstring>