swift234

improve the diagnostics for when a multi-statement closure has no inferred result type.
Previously:

error: generic parameter 'T' could not be inferred
now:
error: unable to infer closure return type in current context

There is still more to do, but this fixes:
<rdar://problem/23570873> QoI: Poor error calling map without being able to infer "U" (closure result inference)