Unbreak build with gcc 4.3: provide missed includes and silence most annoying warnings.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47367 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/FoldingSet.cpp

@@ -17,6 +17,7 @@
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/Support/MathExtras.h"
 #include <cassert>
+#include <cstring>
 using namespace llvm;
 
 //===----------------------------------------------------------------------===//