swift234

Add a pass to specialize array code based on array semantic array.props calls

We know that a native swift array that does not need an element type check is
not going to change to an nsarray, or to an array that needs an element type
check. This allows us to specialize array code.

The array semantic calls 'array.props.isCocoa/needsElementTypeCheck' returns
said array properties for a read.

  func f(a : A[AClass]) {
     for i in 0..a.count {
       let b = a.props.isCocoa()
        .. += _getElement(a, i, b)
     }
  }

   ==>

  func f(a : A[AClass]) {
    let b2 = a.props.isCocoa()
    if (!b2) {
      for i in 0..a.count {
         .. += _getElement(a, i, false)
      }
    } else {
      for i in 0..a.count {
        let b = a.props.isCocoa
        .. += _getElement(a, i, b)
      }
    }
  }

The stdlib will be changed to use array.props calls in a future commit.

rdar://17955309

Swift SVN r23689