With this commit, the `simplifyTerminator` helper function used by IDS
stops trying to merge the default cases with one of the other cases
arbitrarily.
Now, if the `UnreachableSuccessor` was reached via the default case, the
default case is still arbitrarily redirected to an arbitrary case
successor, but the case and the default do not get merged.
This keeps the logic of the transform simpler, and also allows for
easier successive manipulation by planned upcoming transforms.
Pietro Fezzardi
48749974f0