gn: leave PKG_CONFIG_PATH untouched when not using a sysroot

build/config/linux/pkg-config.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.
 
 import json
 import os
 import subprocess
 import sys
 import re
 from optparse import OptionParser
@@ skipping 26 matching lines @@
   print "[[],[],[],[],[]]"
   sys.exit(0)
 
 
 def SetConfigPath(options):
   """Set the PKG_CONFIG_PATH environment variable.
   This takes into account any sysroot and architecture specification from the
   options on the given command line."""
 
   sysroot = options.sysroot
-  if not sysroot:
-    sysroot = ""
+  assert sysroot
 
   # Compute the library path name based on the architecture.
   arch = options.arch
   if sysroot and not arch:
     print "You must specify an architecture via -a if using a sysroot."
     sys.exit(1)
 
   # In the gyp world this is configurable via the 'system_libdir' variable,
   # which doesn't seem to have an equivelent in gn yet.
   # TOOD(sbc): Make this configurable like it is under gyp.
@@ skipping 56 matching lines @@
                   dest='atleast_version', type='string')
 parser.add_option('--libdir', action='store_true', dest='libdir')
 (options, args) = parser.parse_args()
 
 # Make a list of regular expressions to strip out.
 strip_out = []
 if options.strip_out != None:
   for regexp in options.strip_out:
     strip_out.append(re.compile(regexp))
 
-SetConfigPath(options)
 if options.sysroot:
+  SetConfigPath(options)
   prefix = GetPkgConfigPrefixToStrip(args)
 else:
   prefix = ''
 
 if options.atleast_version:
   # When asking for the return value, just run pkg-config and print the return
   # value, no need to do other work.
   if not subprocess.call([options.pkg_config,
                           "--atleast-version=" + options.atleast_version] +
                           args,
@@ skipping 55 matching lines @@
     # this anyway. Removing it here prevents a bunch of duplicate inclusions on
     # the command line.
     pass
   else:
     cflags.append(flag)
 
 # Output a GN array, the first one is the cflags, the second are the libs. The
 # JSON formatter prints GN compatible lists when everything is a list of
 # strings.
 print json.dumps([includes, cflags, libs, lib_dirs, ldflags])