Move TargetFrameLowering.h to CodeGen where it's implemented

This header already includes a CodeGen header and is implemented in
lib/CodeGen, so move the header there to match.

This fixes a link error with modular codegeneration builds - where a
header and its implementation are circularly dependent and so need to be
in the same library, not split between two like this.

llvm-svn: 317379
diff --git a/llvm/lib/CodeGen/TargetOptionsImpl.cpp b/llvm/lib/CodeGen/TargetOptionsImpl.cpp
index ed845e1..99ff493 100644
--- a/llvm/lib/CodeGen/TargetOptionsImpl.cpp
+++ b/llvm/lib/CodeGen/TargetOptionsImpl.cpp
@@ -15,7 +15,7 @@
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Module.h"
-#include "llvm/Target/TargetFrameLowering.h"
+#include "llvm/CodeGen/TargetFrameLowering.h"
 #include "llvm/Target/TargetOptions.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 using namespace llvm;