swift234

[g-arc-opts] Teach the arc optimizer how to recognize more trap BBs in the stdlib.

This reduces the number of retain, release operations in the dylib from 38512 to
16041. That is a reduction of 60%. Most of the code paths affected by this were
in the cocoa part of the stdlib so when I measured the perf test suite I did not
see a huge boost in perf.

rdar://18327670

Swift SVN r21934