We received a bug report at Gentoo that geoclue would not build due to implicit declaration of soup_session_new. This symbol appeared in libsoup-2.42 and is used since geoclue-2.0 it seems.
Please add required version check to configure.
$ git grep "soup_session_new"
src/gclue-web-source.c: priv->soup_session = soup_session_new_with_options
src/geocode-glib/geocode-forward.c: forward->priv->soup_session = soup_session_new ();
src/geocode-glib/geocode-reverse.c: object->priv->soup_session = soup_session_new ();
commit: 8d535cd 8d535cdc7ffe93a769412932d3603673efca5627
Author: Zeeshan Ali (Khattak) <firstname.lastname@example.org>
Date: Wed Nov 12 17:56:41 2014 +0000
Require libsoup >= 2.42
We use API that was introduce in this version so lets explicitly require
this particular version.