swift234

[remove-pin] Teach remove pin how to recognize a safe guaranteed array semantic call sequence.

Given a strong_pin for which we have not yet seen a strong_unpin, a safe
guaranteed call sequence is of the following form:

retain(x)
call f(@guaranteed x)
release(x)

where f is an array semantic call that we know does not touch globals and thus
are known to not change ref counts.

rdar://20305817

Swift SVN r26662