swift234

Make sure that we complete any conformances that are used in the AST.

When semantic analysis forms a reference to a conformance that will
persist in the AST (it is "used" in the C++ odr-used sense), complete
that conformance before type checking terminates. This ensures that
the SIL optimizers have complete conformances to work with for, e.g.,
generic specialization. Fixes rdar://problem/20735544.

Swift SVN r27896