CodeGen: simplify and validate exception personalities

Simplify the dispatching for the personality routines.  This really had
no test coverage previously, so add test coverage for the various cases.
This turns out to be pretty complicated as the various languages and
models interact to change personalities around.

You really should feel bad for the compiler if you are using exceptions.
There is no reason for this type of cruelty.

llvm-svn: 327105