Always honor pkg-config command coming from the user

When building from within a ChromiumOS chroot (and any other
Gentoo-base system), the right command to call pkg-config is specified
up front and needs to be honored. However currently Chromium build
system always calls 'pkg-config' directly if --sysroot is given to the
build. This ignores any necessary setup done by the board sysroot
pkg-config wrapper used on ChromiumOS and causes host's paths being
pulled into the build. Precisely, PKG_CONFIG_PATH is not being unset and
PKG_CONFIG_SYSROOT_DIR is not being set to the sysroot path.

Fix this by always using the specified pkg-config binary, even if
sysroot is given. Even though, the problem could be fixed up by adding
necessary setup to Chromium's pkg-config wrapper, it is not the right
solution, as the setup is inherently sysroot specific and only the
external build system is aware of necessary configuration to be done.

Bug: 743366
Test: Build chromeos-chrome with host's /usr/lib64/pkgconfig/dbus-1.pc chmodded to a-r.
Change-Id: I6e80dbaa94510e31aa5000c6cc31ca32b5e5cbe4
Reviewed-on: https://chromium-review.googlesource.com/572666Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Tomasz Figa <tfiga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487005}

build/config/linux/pkg-config.py

@@ -63,7 +63,7 @@ def SetConfigPath(options):
   return libdir
 
 
-def GetPkgConfigPrefixToStrip(args):
+def GetPkgConfigPrefixToStrip(options, args):
   """Returns the prefix from pkg-config where packages are installed.
 
   This returned prefix is the one that should be stripped from the beginning of
@@ -76,8 +76,8 @@ def GetPkgConfigPrefixToStrip(args):
   # instead of relative to /path/to/chroot/build/x86-generic (i.e prefix=/usr).
   # To support this correctly, it's necessary to extract the prefix to strip
   # from pkg-config's |prefix| variable.
-  prefix = subprocess.check_output(["pkg-config", "--variable=prefix"] + args,
-      env=os.environ)
+  prefix = subprocess.check_output([options.pkg_config,
+      "--variable=prefix"] + args, env=os.environ)
   if prefix[-4] == '/usr':
     return prefix[4:]
   return prefix
@@ -135,7 +135,7 @@ def main():
     libdir = SetConfigPath(options)
     if options.debug:
       sys.stderr.write('PKG_CONFIG_LIBDIR=%s\n' % libdir)
-    prefix = GetPkgConfigPrefixToStrip(args)
+    prefix = GetPkgConfigPrefixToStrip(options, args)
   else:
     prefix = ''
 

build/config/linux/pkg_config.gni

@@ -51,21 +51,23 @@ 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.
+pkg_config_args = []
+
 if (sysroot != "") {
   # Pass the sysroot if we're using one (it requires the CPU arch also).
-  pkg_config_args = [
+  pkg_config_args += [
     "-s",
     rebase_path(sysroot),
     "-a",
     current_cpu,
   ]
-} else if (pkg_config != "") {
-  pkg_config_args = [
+}
+
+if (pkg_config != "") {
+  pkg_config_args += [
     "-p",
     pkg_config,
   ]
-} else {
-  pkg_config_args = []
 }
 
 # Only use the custom libdir when building with the target sysroot.