Plumb system_libdir variable from GN to pkg-config.py

build/config/linux/pkg_config.gni

 # 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.
 
 import("//build/config/sysroot.gni")
 
 # Defines a config specifying the result of running pkg-config for the given
 # packages. Put the package names you want to query in the "packages" variable
 # inside the template invocation.
 #
@@ skipping 13 matching lines @@
 # when doing manual dynamic linking), set:
 #   ignore_libs = true
 
 declare_args() {
   # A pkg-config wrapper to call instead of trying to find and call the right
   # pkg-config directly. Wrappers like this are common in cross-compilation
   # environments.
   # Leaving it blank defaults to searching PATH for 'pkg-config' and relying on
   # the sysroot mechanism to find the right .pc files.
   pkg_config = ""
+
+  # CrOS builds set the `system_libdir` variable as part of building on a 64 or

[brettw, 2016/01/07 00:43:25]

I'm a bit confused what "lib" is relative to. The root directory? The sysroot?
It would be goot to mention that here an in the python script.

[rjkroege, 2016/01/07 01:37:37]

Done. Much more detailed comment now.

+  # 32 bit target.
+  system_libdir = "lib"
 }
 
 pkg_config_script = "//build/config/linux/pkg-config.py"
 
 # Define the args we pass to the pkg-config script for other build files that
 # need to invoke it manually.
 if (sysroot != "") {
   # Pass the sysroot if we're using one (it requires the CPU arch also).
   pkg_config_args = [
     "-s",
     sysroot,
     "-a",
     current_cpu,
+    "--system_libdir",
+    system_libdir,
   ]
 } else if (pkg_config != "") {
   pkg_config_args = [
     "-p",
     pkg_config,
+    "--system_libdir",
+    system_libdir,
   ]
 } else {
   pkg_config_args = []
 }
 
 template("pkg_config") {
   assert(defined(invoker.packages),
          "Variable |packages| must be defined to be a list in pkg_config.")
   config(target_name) {
     args = pkg_config_args + invoker.packages
@@ skipping 11 matching lines @@
       ldflags = pkgresult[4]
     }
 
     forward_variables_from(invoker,
                            [
                              "defines",
                              "visibility",
                            ])
   }
 }