Apply changes to migrate to upstream

- Following constants have been removed by the upstream,
  so we have to define our version.

  - bitc::FUNC_CODE_INST_UNWIND
  - Intrinsic::eh_exception
  - Intrinsic::eh_selector

- 'unwind' instruction has been removed by upstream.
  Emitting 'landingpad' and 'resume' instead when readers
  find 'unwind' instructions in bitcode.

- llvm::Attribute now is a class, not unsigned.
  Adjust the way to use llvm::Attribute according to upstream.

Change-Id: Iecefbc17e29093e09ada60c928cc951de681ea98
3 files changed