Introduce dart_host_toolchain arg, remove '--checked' option from patch_sdk.py

utils/generate_patch_sdk.gni

 # Copyright (c) 2017, 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("../build/prebuilt_dart_sdk.gni")
+import("../build/dart_host_toolchain.gni")
 
 _dart_root = get_path_info("..", "abspath")
 
 # Template to generate a patched_sdk folder. This invokes the tools/patch_sdk.py
 # script and sets up the right dependencies.
 #
 # This template expects four arguments:
 #   - mode: vm or dart2js (whether to build an sdk for the vm or for dart2js)
 #   - input_patches_dir: directory containing the input library files.
 #   - patched_sdk_dir: the output location
 #   - deps: extra dependencies that must be built ahead of time.
 template("generate_patched_sdk") {
   assert(defined(invoker.input_patches_dir),
          "Need input_patches_dir in $target_name")
   assert(defined(invoker.patched_sdk_dir),
          "Need patched_sdk_dir in $target_name")
   assert(defined(invoker.mode), "Need mode in $target_name")
   action(target_name) {
     if (defined(invoker.deps)) {
       deps = invoker.deps
     } else {
       deps = []
     }
 
     if (!prebuilt_dart_exe_works) {
-      deps += [ "$_dart_root/runtime/bin:dart_bootstrap($host_toolchain)" ]
+      deps += [ "$_dart_root/runtime/bin:dart_bootstrap_host_arch($dart_host_toolchain)" ]
     }
 
     script = "$_dart_root/tools/patch_sdk.py"
 
     # We list the `patch_sdk.dart` tool here because the [script] (which is
     # implicitly an input) will call it.
     inputs = [
       "$_dart_root/tools/patch_sdk.dart",
     ]
 
     depfile = "$root_out_dir/${target_name}.d"
 
     outputs = [
       # Instead of listing all outputs we list a single well-known one.
       "$root_out_dir/${invoker.patched_sdk_dir}/platform.dill",
     ]
 
     args = [ "--quiet" ]
     if (!prebuilt_dart_exe_works) {
       dart_out_dir = get_label_info(
-              "$_dart_root/runtime/bin:dart_bootstrap($host_toolchain)",
+              "$_dart_root/runtime/bin:dart_bootstrap_host_arch($dart_host_toolchain)",
               "root_out_dir")
       dart_bootstrap =
           rebase_path("$dart_out_dir/dart_bootstrap$executable_suffix")
       args += [
         "--dart-executable",
         dart_bootstrap,
       ]
     }
     args += [
       invoker.mode,
       rebase_path("$_dart_root/sdk"),
       rebase_path(invoker.input_patches_dir),
       rebase_path("$root_out_dir/${invoker.patched_sdk_dir}", root_build_dir),
       rebase_path("$_dart_root/.packages"),
     ]
   }
 }