Fix Linux build.

Author: millenomi

TestFoundation/TestFileManager.swift

@@ -7,7 +7,9 @@
 // See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 
-#if !DEPLOYMENT_RUNTIME_OBJC
+#if !DEPLOYMENT_RUNTIME_OBJC && (os(Linux) || os(Android))
+@testable import Foundation
+#else
 @testable import SwiftFoundation
 #endif