swift234

Sema: Another fix for protocol self-conformance

It looks like we were checking in the wrong place, as a result we didn't
catch stuff like

class G<T : AnyObject> {}
_ = G<P>()

This would crash later in IRGen.

Make the conformsToProtocol() check do the right thing, and remove some
other miscellaneous diagnostics in the process. Also, make the
"type 'T' does not conform to protocol 'P'" diagnostic a bit more
detailed.

Unfortunately in a few instances we lose a more descriptive diagnostic to
a general 'cannot invoke 'foo' with argument list of type 'T'' error. The
argument matching diagnostics need to be addressed anyway though.

Fixes <rdar://problem/20311619>.

Swift SVN r29737