swift234

Sema: Fix problems with coerceClosureExprToVoid()

- If the closure being rewritten was nested inside of another
  closure, we would rewrite the nested closure into a new closure
  having cs.DC as its parent, rather than the DeclContext of the
  outer closure as required.

- If the closure being rewritten had nested closures, the parent
  DeclContext of the nested closures was set to the old closure,
  not the new one.

Fix both problems by having coerceClosureExprToVoid() modify the
closure in place instead of creating a new closure.

Fixes <rdar://problem/20931915>.

Swift SVN r29563