[SwiftArray] Don't assume pointer size is 8.
[SwiftArray] Don't assume pointer size is 8.

Fixes yet another failure visible only on 32-bits architectures.
(TestSwiftieFormatting/TestNestedArray)

<rdar://problem/47272296>
<rdar://problem/47271440>

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb