swift234

IRGen: Set integer extension attributes on external arguments.

Clean up the messy code for putting byval arguments at the right argument index; we don't pretend to handle multiple uncurry levels in IRGen anymore, so we can just use the absolute index of lowered arguments for attribute indices. Add zeroext/signext attributes as needed for small integer arguments in calls. Fixes rdar://problem/19455987.

Swift SVN r25687