Fix previous CL where dart_bootstrap was accidently changed to dart_bootstrap_host_arch

BUILD.gn

 # 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("build/dart_host_toolchain.gni")
+
 # This target will be built if no target is specified when invoking ninja.
 group("default") {
   if (is_fuchsia || is_fuchsia_host) {
     # Fuchsia has run_vm_tests marked testonly.
     testonly = true
   }
   deps = [
     ":runtime",
   ]
 }
@@ skipping 14 matching lines @@
   ]
 }
 
 group("runtime") {
   if (is_fuchsia || is_fuchsia_host) {
     # Fuchsia has run_vm_tests marked testonly.
     testonly = true
   }
   deps = [
     "runtime/bin:dart",
-    "runtime/bin:dart_bootstrap($host_toolchain)",
+    "runtime/bin:dart_bootstrap($dart_host_toolchain)",
     "runtime/bin:process_test",
     "runtime/bin:run_vm_tests",
     "runtime/bin:sample_extension",
     "runtime/bin:test_extension",
     "runtime/vm:patched_sdk",
   ]
 }
 
 group("runtime_kernel") {
   if (is_fuchsia || is_fuchsia_host) {
     # Fuchsia has run_vm_tests marked testonly.
     testonly = true
   }
   deps = [
     ":runtime",
 
     # TODO(rmacnak): Link this into 'dart'.
     "utils/kernel-service:kernel-service",
   ]
 }
 
 group("runtime_precompiled") {
   deps = [
-    "runtime/bin:dart_bootstrap($host_toolchain)",
+    "runtime/bin:dart_bootstrap($dart_host_toolchain)",
     "runtime/bin:dart_precompiled_runtime",
     "runtime/bin:process_test",
     "runtime/vm:patched_sdk",
   ]
 }
 
 group("create_sdk") {
   deps = [
     "sdk:create_sdk",
   ]
@@ skipping 120 matching lines @@
       rebase_path(input),
       "--output-file",
       rebase_path(output),
       "--build-id-map",
       rebase_path("$target_gen_dir/build_id_map"),
       "--pre-binaries",
       rebase_path(magenta_bootdata),
     ]
   }
 }