Add 129518 back with a fix for when we are producing eh just because of debug info.

Add 129518 back with a fix for when we are producing eh just because of debug info.
Change ELF systems to use CFI for producing the EH tables. This reduces the
size of the clang binary in Debug builds from 690MB to 679MB.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129571 91177308-0d34-0410-b5e6-96231b3b80d8