Now that the core codegen support has been implemented in LLVM, we can
start using it in Clang.
This allows us to generate more efficient and smaller code for
For now, we only enable this for the Itanium EH handling,
_gxx_personality_v0 and _objc_personality_v0, as LLVM support is still
incomplete for other exception-handling schemes.
Depends on D141917