swift234

Rework processing of @noescape closures a bit to fix rdar://19981118:
- Have Sema, not SILGen decide if a vardecl can be captured by address
  instead of by-box.  This is a non-local property that is best computed
  during capture set formation.  Sema captures this as a bit on the new
  CapturedValue entry.
- Rework some diagnostic emission to centralize a class of noescape 
  diagnostics in capture set calculation.  Previously, funcdecl closures
  produced their diagnostics there, but ClosureExprs produced them in
  MiscDiagnostics (NFC for this part).

This fixes <rdar://problem/19981118> Swift 1.2 beta 2: Closures nested in @noescape closures copy, rather than reference, captured vars.



Swift SVN r25759