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

build/config/linux/dbus/BUILD.gn

 # Copyright 2016 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.
 
 import("//build/config/linux/pkg_config.gni")
 
-pkg_config("system_libxml") {
-  packages = [ "libxml-2.0" ]
+# Note: if your target also depends on //dbus, you don't need to add this
+# config (it will get added automatically if you depend on //dbus).
+pkg_config("dbus") {
+  packages = [ "dbus-1" ]
 }
-
-static_library("libxml") {
-  sources = [
-    "chromium/libxml_utils.cc",
-    "chromium/libxml_utils.h",
-  ]
-
-  public_configs = [ ":system_libxml" ]
-}