[update_engine] use libchromeos.pc

BUG=chromium-os:24959
TEST=build

Signed-off-by: Elly Jones <ellyjones@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/14021
Reviewed-by: Mike Frysinger <vapier@chromium.org>
(cherry picked from commit cdd107e1d16fe05ad11140b690bdda6695e0bc6e)

Change-Id: I39f644af99f2ee4a14b4a1108483e5dbf005e786
Reviewed-on: https://gerrit.chromium.org/gerrit/14516
Reviewed-by: Kees Cook <keescook@chromium.org>
Commit-Ready: Elly Jones <ellyjones@chromium.org>
Tested-by: Elly Jones <ellyjones@chromium.org>
diff --git a/SConstruct b/SConstruct
index d73c4e8..bda72dc 100644
--- a/SConstruct
+++ b/SConstruct
@@ -223,7 +223,7 @@
 pkgconfig = os.environ.get('PKG_CONFIG', 'pkg-config')
 
 env.ParseConfig(pkgconfig + ' --cflags --libs '
-                'dbus-1 dbus-glib-1 gio-2.0 gio-unix-2.0 glib-2.0')
+                'dbus-1 dbus-glib-1 gio-2.0 gio-unix-2.0 glib-2.0 libchromeos')
 env.ProtocolBuffer('update_metadata.pb.cc', 'update_metadata.proto')
 env.PublicKey('unittest_key.pub.pem', 'unittest_key.pem')
 env.PublicKey('unittest_key2.pub.pem', 'unittest_key2.pem')