Replace '#include ValueTypes.h' with forward declarations.

In some cases the include is pushed "downstream" (or removed if
unused).

llvm-svn: 203644
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index be2913d..66835bf 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -18,7 +18,6 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/CodeGen/SelectionDAGNodes.h"
-#include "llvm/CodeGen/ValueTypes.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -57,6 +56,7 @@
 class MachineInstr;
 class MachineRegisterInfo;
 class MDNode;
+class MVT;
 class PHINode;
 class PtrToIntInst;
 class ReturnInst;