Use withUnsafeMutableBufferPointer in NSData test.

This ensures that:
- We produce a well scoped stable pointer for the duration of the use.

- We aren't attempting to do an implicit conversion from an array to
  pointer in an argument position which is an autoclosure result,
  which is now disallowed in
  swiftlang/swift#16623.

Author: rudkx

TestFoundation/TestNSData.swift

@@ -1,6 +1,6 @@
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2016, 2018 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See http://swift.org/LICENSE.txt for license information
@@ -600,10 +600,15 @@ class TestNSData: LoopbackServerTest {
 
     func test_edgeNoCopyDescription() {
         let expected = "<ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ... ffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ff>"
-        let bytes = [UInt8](repeating: 0xff, count: 1025)
-        let data = NSData(bytesNoCopy: UnsafeMutablePointer(mutating: bytes), length: bytes.count, freeWhenDone: false)
-        XCTAssertEqual(data.debugDescription, expected)
-        XCTAssertEqual(data.bytes, bytes)
+        var bytes = [UInt8](repeating: 0xff, count: 1025)
+
+        bytes.withUnsafeMutableBufferPointer {
+            let baseAddress = $0.baseAddress!
+            let count = $0.count
+            let data = NSData(bytesNoCopy: UnsafeMutableRawPointer(baseAddress), length: count, freeWhenDone: false)
+            XCTAssertEqual(data.debugDescription, expected)
+            XCTAssertEqual(data.bytes, UnsafeRawPointer(baseAddress))
+        }
     }
 
     func test_initializeWithBase64EncodedDataGetsDecodedData() {