[ubsan] Implement the -fcatch-undefined-behavior flag using a trapping
implementation; this is much more inline with the original implementation
(i.e., pre-ubsan) and does not require run-time library support.

The trapping implementation can be invoked using either '-fcatch-undefined-behavior'
or '-fsanitize=undefined-trap -fsanitize-undefined-trap-on-error', with the latter
being preferred.  Eventually, the -fcatch-undefined-behavior' flag will be removed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173848 91177308-0d34-0410-b5e6-96231b3b80d8