This fixes a regression from the previous patch which got
rid of PrintOptions::StripDynamicSelf.
When printing protocol declarations with a BaseType set in
PrintOptions, we can end up with a DynamicSelfType wrapping
a non-class type, if the protocol requirement returned
Self.
Note that this changes the diagnostic for missing protocol
requirements slightly; we used to sometimes refer to 'Self'
even if the conforming type is not a class, which is not
accepted by the type checker anyway. I believe the new
diagnostics are more correct.
1df6e51c14