Fix counters for regions following `else if`s, fix
the counters for `else if` conditions, and fix
handling of `break` statements. Also while here,
clean up the handling of branch exit regions such
that we don't generate multiple overlapping
regions for each branch, but a single region at
the end of the entire `if` statement that accounts
for all exiting control flow.
rdar://104078910
rdar://104079242
c3b055a9a8