swift234

Expand the no-return diagnostic

Turn on the noreturn diagnostic for cases where a reachable unreachable
could be encountered.  Previously, the diagnostic would not fire if the
function was marked noreturn and any of its reachable unreachable calls
were around.  While this makes sense from a SILGen perspective (it Just
Crashes tm), it is still wrong.  We need to diagnose *everything* that
has reachable unreachables.