[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.

llvm-svn: 173848