swift234

Prohibit specialization on DynamicSelf type.

Fixes <rdar://problem/20044992> Swift: Generic functions called from
class methods with type parameter inferred to Self compiles, breaks
type system under optimization

If we don't prohibit specialization then we silently miscompile by
assuming a base class instead of the dynamic type.

It is unclear to me why GenericFunctionType did not inherit any
recursive type properties from it's arguments and result. However, it
I think it makes sense to propagate DynamicSelfType into
GenericFunctionType so I've broke with convention here.

Swift SVN r28541