build: Add cleanup functions

Since it's just using this one header from libgsystem for now, just copy the
header file instead of using a git submodule.

(cherry picked from commit e9cab814892fc5b697e7574a827ac4d5e16f2b3b)
(cherry picked from commit 5283674716dd8b2cd94c4d95ee127cab81c76503)
all: Do not use '&s' format with g_variant_get

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=708198 and
https://bugzilla.redhat.com/show_bug.cgi?id=1036374 .

(cherry picked from commit ac62dbbda2630d1d963d399317d59cf7b78dc7f2)
screen: Allow man: links containing hyphens

https://bugzilla.redhat.com/show_bug.cgi?id=1040713
(cherry picked from commit c089b0583ddd5acc3e9d72c45f94747e6316239a)
(cherry picked from commit 13842c2e70a3018b2da09273d16eadd9666dfe74)