Fix previous CL where dart_bootstrap was accidently changed to dart_bootstrap_host_arch

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 6b0eb2ed56f3be3f500ced9698e8b7c44c7639e2..5671590c18ec5fe63564fc71de9e277003fed869 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2,6 +2,8 @@
 # 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) {
@@ -36,7 +38,7 @@ group("runtime") {
   }
   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",
@@ -60,7 +62,7 @@ group("runtime_kernel") {
 
 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",