Use current glib thread functions when available

Kept deprecated code for users of old glib by using version checks.

Documentation: https://developer.gnome.org/glib/2.34/glib-Deprecated-Thread-APIs.html
See-also: https://developer.gnome.org/glib/stable/glib-Version-Information.html#GLIB-CHECK-VERSION:CAPS
Fixes: warning: ‘g_static_mutex_get_mutex_impl’ is deprecated: Use 'GMutex' instead [-Wdeprecated-declarations]
Fixes: warning: ‘g_thread_create’ is deprecated: Use 'g_thread_new' instead [-Wdeprecated-declarations]
Fixes: warning: ‘g_type_init’ is deprecated [-Wdeprecated-declarations]
Cleanup-by: Paul Wise <pabs3@bonedaddy.net>