libgtk3: bump to 3.14.4

Bump libgtk3 to version 3.14.4.

Also add a patch to fix compilation of a build tool: extract-strings.
The bug has already been reported [1], but no proper resolution has been
provided yet. This patch only covers the Buildroot issue.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=731013



[Thomas: fix minor typo in the description of the newly added patch.]

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>