Use DarwinToolchain for apple-none targets

- When compiling for os none for apple, we should perfer using a Darwin
  toolchain (maybe a misnomer now) instead of a generic UNIX toolchain.
  This results in the driver selecting relevant tools for apple
  platforms, such as using ld64 over gold, etc.

Author: rauhul

Sources/SwiftDriver/Driver/Driver.swift

@@ -2954,12 +2954,19 @@ extension Triple {
       return DarwinToolchain.self
     case .linux:
       return GenericUnixToolchain.self
-    case .freeBSD, .haiku, .openbsd, .noneOS:
+    case .freeBSD, .haiku, .openbsd:
       return GenericUnixToolchain.self
     case .wasi:
       return WebAssemblyToolchain.self
     case .win32:
       return WindowsToolchain.self
+    case .noneOS:
+        switch self.vendor{
+        case .apple:
+            return DarwinToolchain.self
+        default:
+            return GenericUnixToolchain.self
+        }
     default:
       diagnosticsEngine.emit(.error_unknown_target(triple))
       throw Driver.ErrorDiagnostics.emitted