swift234

Broaden the "favored constraint" binop optimization to work with simplified expression types, and not just default literal tyvars.

This addresses or improves several existing TC perf bugs (rdar://problem/15933674, rdar://problem/17110608, rdar://problem/17240816, rdar://problem/17244974), and seems to speed up our unit test runs by ~5%. (On my MacBook Pro, total average execution time is reduced from 557.28s to 531.89s.)

Swift SVN r19939