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/Target/X86/X86FrameLowering.h b/llvm/lib/Target/X86/X86FrameLowering.h
index 38ac96e..909319f 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.h
+++ b/llvm/lib/Target/X86/X86FrameLowering.h
@@ -14,7 +14,7 @@
 #ifndef LLVM_LIB_TARGET_X86_X86FRAMELOWERING_H
 #define LLVM_LIB_TARGET_X86_X86FRAMELOWERING_H
 
-#include "llvm/Target/TargetFrameLowering.h"
+#include "llvm/CodeGen/TargetFrameLowering.h"
 
 namespace llvm {