Add support for sysroots to GN's pkg-config.

build/config/linux/sysroot_ld_path.py

+# 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 file takes two arguments, the relative location of the shell script that
+# does the checking, and the name of the sysroot.
+
+# TODO(brettw) the build/linux/sysroot_ld_path.sh script should be rewritten in
+# Python in this file.
+
+import subprocess
+import sys
+
+if len(sys.argv) != 3:
+  print "Need two arguments"
+  sys.exit(1)
+
+result = subprocess.check_output([sys.argv[1], sys.argv[2]]).strip()
+
+print '"' + result + '"'