Fix Flutter mac build

runtime/bin/BUILD.gn

 # Copyright (c) 2014, 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.
 
 
 declare_args() {
   dart_io_support = false
 
   # TODO(zra, jamesr): Remove this check once we start building boringssl for
   # the fuchsia port.
@@ skipping 203 matching lines @@
 
 if ((current_toolchain == host_toolchain) ||
     (!defined(is_fuchsia) || !is_fuchsia)) {
 io_impl_sources_gypi =
     exec_script("../../tools/gypi_to_gn.py",
                 [ rebase_path("io_impl_sources.gypi") ],
                 "scope",
                 [ "io_impl_sources.gypi" ])
 }
 
-if (current_toolchain == host_toolchain) {
+if (!defined(is_fuchsia) || (current_toolchain == host_toolchain)) {
 
 executable("gen_snapshot") {
   configs += ["..:dart_config",
               "..:dart_product_config",
               "..:dart_precompiler_config"]
   deps = [
     ":gen_resources_cc",
     ":gen_snapshot_dart_io",
     ":generate_builtin_cc_file",
     ":generate_io_cc_file",
@@ skipping 225 matching lines @@
       "..",
       "../include"
     ]
 
     deps = [
       ":dart_snapshot_cc",
       ":libdart_embedder_noio",
     ]
   }
 }