🐳 Move linux pkg_config() calls into separate BUILD.gn files

BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 874 matching lines @@
 
 # For compatibility with GYP. The linux_chromium_chromeos_rel_ng and
 # linux_chromium_chromeos_compile_rel_ng bots reference this target as
 # something to build, but all targets for those bots to compile are set
 # up differently.
 # TODO bug 601920: Remove reference to aura_builder on bot config and delete
 # this group.
 group("aura_builder") {
 }
 
+if (is_android) {
+  group("optimize_gn_gen") {
+    deps = [
+      # These run expensive scripts in non-default toolchains. Generally, host
+      # toolchain targets are loaded in the later part of the run, and the
+      # result is they push out the end of generation. By preloading these, the
+      # scripts can be parallelized with the rest of the load.
+      "//build/config/linux(//build/toolchain/linux:clang_x64)",
+      "//build/config/posix(//build/toolchain/linux:clang_x64)",
+
+      # Include x86 toolchains as well since V8 uses them for 32-bit snapshot
+      # generation.
+      "//build/config/linux(//build/toolchain/linux:clang_x86)",
+      "//build/config/posix(//build/toolchain/linux:clang_x86)",
+    ]
+  }
+}
+
 # Because of the source assignment filter, many targets end up over-filtering
 # their sources if the output directory contains a platform name. Assert that
 # this doesn't happen. http://crbug.com/548283
 template("assert_valid_out_dir") {
   # List copied from //build/config/BUILDCONFIG.gn.
   set_sources_assignment_filter([
                                   "*\bandroid/*",
                                   "*\bchromeos/*",
                                   "*\bcocoa/*",
                                   "*\bios/*",
                                   "*\blinux/*",
                                   "*\bmac/*",
                                   "*\bposix/*",
                                   "*\bwin/*",
                                 ])
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }