Bug 1427337 - Fix build config bustage from the fallout from bug 1426758 r=frg

suite/config/mozconfigs/mozconfig.linux.common

@@ -1,5 +1,9 @@
 # Common statements that are applicable to both Linux32 and Linux64.
 
+# Due to bug 1426758, we need to re-include mozconfig.gtk with our
+# linux* builders.
+. ${TOOLTOOL_DIR}/build/unix/mozconfig.gtk
+
 ac_add_options --with-google-api-keyfile=/builds/google-api.key
 
 # SeaMonkey uses the google api key for Geolocation services