swift234

Fix <rdar://problem/19773562> Closures executed immediately { like this }() are not automatically @noescape

In addition to being better for performance in these cases, this disables the "self." 
requirement in these blocks.  {}() constructs are often used to work around statements
that are not exprs in Swift, so they are reasonably important.

Fixing this takes a couple of pieces working together:
 - Add a new 'extraFunctionAttrs' map to the ConstraintSystem for solution
   invariant function attributes that are inferred (like @noescape).
 - Teach constraint simplification of function applications to propagate 
   @noescape between unified function types.
 - Teach CSGen of ApplyExprs to mark the callee functiontype as noescape
   when it is obviously a ClosureExpr.

This is a very limited fix in some ways: you could argue that ApplyExpr should
*always* mark its callee as noescape.  However, doing so would just introduce a
ton of function conversions to remove it again, so we don't do that.




Swift SVN r27723