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

build/config/linux/pangocairo/BUILD.gn

Index: build/config/linux/pangocairo/BUILD.gn
diff --git a/services/user/public/cpp/BUILD.gn b/build/config/linux/pangocairo/BUILD.gn
similarity index 61%
copy from services/user/public/cpp/BUILD.gn
copy to build/config/linux/pangocairo/BUILD.gn
index f341a18b19af81ef3555e0516a57d41519a3b99b..727b52d53335976b87de4d4965ec5edd02fd02ba 100644
--- a/services/user/public/cpp/BUILD.gn
+++ b/build/config/linux/pangocairo/BUILD.gn
@@ -2,9 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("cpp") {
-  sources = [
-    "constants.cc",
-    "constants.h",
-  ]
+import("//build/config/linux/pkg_config.gni")
+
+pkg_config("pangocairo") {
+  packages = [ "pangocairo" ]
 }