stdlib: Use config directives to work without objective-c.

Swift SVN r23211

stdlib/core/SwiftNativeNSArray.swift

@@ -18,6 +18,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if _runtime(_ObjC)
 import SwiftShims
 
 /// Return true iff the given `index` is valid as a position, i.e. `0
@@ -218,11 +219,16 @@ extension _SwiftNativeNSArrayWithContiguousStorage: _NSArrayCoreType {
       ?? _nativeStorage._getNonVerbatimBridgedCount()
   }
 }
+#else
+// Empty shim version for non-objc platforms.
+class _SwiftNativeNSArrayWithContiguousStorage {}
+#endif
 
 /// Base class of the heap buffer backing arrays.  
 internal class _ContiguousArrayStorageBase
   : _SwiftNativeNSArrayWithContiguousStorage {
 
+#if _runtime(_ObjC)
   internal override func withUnsafeBufferOfObjects<R>(
     body: (UnsafeBufferPointer<AnyObject>)->R
   ) -> R {
@@ -253,6 +259,7 @@ internal class _ContiguousArrayStorageBase
     _sanityCheckFailure(
       "Concrete subclasses must implement _getNonVerbatimBridgedHeapBuffer")
   }
+#endif
 
   func canStoreElementsOfDynamicType(_: Any.Type) -> Bool {
     _sanityCheckFailure(