This would just set the NominalTypeDecl's declared type to
ErrorType, which caused problems elsewhere.
Instead, generalize the logic used for AbstractFunctionDecl.
This correctly wires up the GenericTypeParamDecl's archetypes even
if the signature didn't validate, fixing crashes if the generic
parameters of the type are referenced.
Cleans up AST printing somewhat as well as providing slightly better
type-to-declaration mappings for annotated AST printing and indexing.
Swift SVN r32420
