GN: Don't depend on dart_bootstrap if there is a usable prebuilt sdk

build/executable_suffix.gni

 # Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-import("../invoke_dart.gni")
-
-application_snapshot("analysis_server") {
-  main_dart = "../../pkg/analysis_server/bin/server.dart"
-  training_args = [ "--help" ]
+if (defined(is_win) && is_win) {
+  executable_suffix = ".exe"
+} else {
+  executable_suffix = ""
 }