Tajik translation updated
build: Add configure option to enable -Bsymbolic

We should always compile with -Bsymbolic enabled to avoid intra-library
PLT jumps.

https://bugzilla.gnome.org/show_bug.cgi?id=703734
Use new macros when compiling against new GLib

If we're being compiled against a newer version of GLib, we should use
the new macros that add instance private data.

Since this is a stable branch, we cannot bump the GLib requirement; so
we use version checks to conditionally compile the new code.