Avoid ASTContext.h -> TargetInfo.h dep
This has been done before in 2008:
ab13857072
But these things regress easily.
Move some things out of line.
Saves 316 includes + transitive stuff:
316 - ../clang/include/clang/Basic/TargetOptions.h
316 - ../clang/include/clang/Basic/TargetInfo.h
316 - ../clang/include/clang/Basic/TargetCXXABI.h
316 - ../clang/include/clang/Basic/OpenCLOptions.h
316 - ../clang/include/clang/Basic/OpenCLExtensions.def
302 - ../llvm/include/llvm/Target/TargetOptions.h
302 - ../llvm/include/llvm/Support/CodeGen.h
302 - ../llvm/include/llvm/MC/MCTargetOptions.h
302 - ../llvm/include/llvm/ADT/FloatingPointMode.h
302 - ../clang/include/clang/Basic/XRayInstr.h
302 - ../clang/include/clang/Basic/DebugInfoOptions.h
302 - ../clang/include/clang/Basic/CodeGenOptions.h
302 - ../clang/include/clang/Basic/CodeGenOptions.def
257 - ../llvm/include/llvm/Support/Regex.h
79 - ../llvm/include/llvm/ADT/SmallSet.h
68 - MSVCSTL/include/set
66 - ../llvm/include/llvm/ADT/SmallPtrSet.h
62 - ../llvm/include/llvm/ADT/StringSwitch.h