swift234

Protocol conformance: handle derivable requirements before same-named requirements.

Other protocols can have requirements that match up with the
requirements of derivable protocols. In such cases, deriving the
requirement we know about *first* can mean that it will be used to
satisfy the requirement of some other protocol. This behavior has
always been order-dependent before, and the order changed in Swift 2.0
with the introduction of the protocol conformance table, causing
rdar://problem/22476643.

Now, when we see a requirement that looks like a derivable
requirement, go ahead and satisfy the witness for that derivable
requirement. This will, when needed, synthesize an actual witness for
the derivable requirement---that can also be used for the original
requirement---eliminating the ordering dependency and fixing
rdar://problem/22476643.

Swift SVN r32191