swift234

Extend the hack that delays enum conformance checking to code-completion

This works around a big performance regression in code completion
performance that was introduced with r25741.  This hack does not work
completely correctly with multiple file builds, but a) this should be a
minor issue for enum code completions, and b) this simply returns to the
pre-25741 behaviour.  This hack should disappear when we fix
rdar://problem/20047340.

For rdar://problem/20445407.

Swift SVN r27320