[CodeExtractor] Mark functions noreturn when applicable

This eliminates the outlining penalty for llvm.trap/unreachable, because
callers no longer have to emit cleanup/ret instructions after calling an
outlined `noreturn` function.

rdar://45523626

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346421 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed