[LLVM up] Add basic -S option to clang.
 - Split backend related consumer out into Backend.cpp, replaces
   LLVMCodeGenWriter.
 - Structure follows llvm-gcc to some extent.
 - Still need to implement all the options which impact code
   generation and the optimization passes which llvm-gcc uses at
   various levels.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57936 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed