glib: Enable make check

Glib tests needed TZDIR set for gdatetime.c test, then the lib path for finding libgcc_s, and the path to libglib .so (don't know exactly why make didn't peek it automatically, shouldn't be an upstream issue).
Only one test remaining due to https://bugzilla.gnome.org/show_bug.cgi?id=724412 : they create temp files in $HOME/.cache , hope that gets fixed upstream.
I'm not sure if buildInputs is the right place for tzdata.