Synchronize gen_snapshot sources in bin/BUILD.gn with bin.gypi

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
 }
 
 
@@ skipping 133 matching lines @@
 executable("gen_snapshot") {
   configs += ["..:dart_config"]
   deps = [
     ":libdart_withcore",
     ":libdart_builtin",
   ]
 
   sources = [
     "gen_snapshot.cc",
     # Very limited native resolver provided.
+    "builtin_common.cc",
     "builtin_gen_snapshot.cc",
     "builtin.cc",
     "builtin.h",
+    "platform_android.cc",
+    "platform_linux.cc",
+    "platform_macos.cc",
+    "platform_win.cc",
+    "platform.h",
     # Include generated source files.
     "$target_gen_dir/builtin_gen.cc",
     "$target_gen_dir/io_gen.cc",
     "$target_gen_dir/io_patch_gen.cc",
   ]
 
   include_dirs = [
     "..",
   ]
 }
 
 
 static_library("libdart_embedder_noio") {
   configs += ["..:dart_config",]
   deps = [
     "..:libdart",
     "../vm:libdart_platform",
   ]
 }