Add includes to get ptrdiff_t. This is needed by gcc-4.6 which has

done some more header trimming, resulting in cstdef being included
by less header files.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105786 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/DenseMap.h

@@ -22,6 +22,7 @@
 #include <new>
 #include <utility>
 #include <cassert>
+#include <cstddef>
 #include <cstring>
 
 namespace llvm {

include/llvm/ADT/SmallVector.h

@@ -17,6 +17,7 @@
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
 #include <cassert>
+#include <cstddef>
 #include <cstdlib>
 #include <cstring>
 #include <memory>

include/llvm/ADT/ilist.h

@@ -39,6 +39,7 @@
 #define LLVM_ADT_ILIST_H
 
 #include <cassert>
+#include <cstddef>
 #include <iterator>
 
 namespace llvm {

include/llvm/Use.h

@@ -27,6 +27,7 @@
 
 #include "llvm/Support/Casting.h"
 #include "llvm/ADT/PointerIntPair.h"
+#include <cstddef>
 #include <iterator>
 
 namespace llvm {