swift234

Make same-type requirements prefer to be rooted at outer generic parameters.

All archetypes from outer scopes are fixed (as a lame implementation
restriction), so same-type constraints that involve archetypes from
outer scopres should treat the archetypes from outer scopes as the
representative. Do so, and start eliminating the notion of a "primary"
archetype that was preventing this fix from occurring earlier, so that
"all archetypes" and the set of requirements generated from the
archetype builder still line up.

Fixes rdar://problem/19519590.

Swift SVN r29869