Enable CFI on OS X.

Enable CFI on OS X.
Currently the output should be almost identical to the one produced by CodeGen
to make the transition easier.

The only two differences I know of are:

* Some files get an extra advance loc of size 0. This will be fixed when
relaxations are enabled.
* The optimization of declaring an EH symbol as an external variable is not
implemented. This is a subset of adding the nounwind attribute, so we if really
this at -O0 we should probably do it at the IL level.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130623 91177308-0d34-0410-b5e6-96231b3b80d8