c++-gtk-utils: Update to 2.2.19

Changelog:
Version 2.2.19 (27 January 2020)
--------------

        Use autoconf's TAP support for running tests (Makefile.am,
        configure-gtk2.ac, configure-gtk3.ac, configure-gtk4.ac;
        c++-gtk-utils/Makefile.am; docs/Makefile.am; tests/Makefile.am,
        tests/extension/Makefile.am, tests/extra/Makefile.am; removed -
        Makefile.decl; added - glib-tap.mk, tap-driver.sh, tap-test,
        m4/glibtests.m4)

        Cater for guile-3.0 declarative modules (acinclude.m4;
        extension.h).

        Suppress GStaticRecMutex deprecation warnings (acinclude.m4,
        configure-gtk2.ac, configure-gtk3.ac, configure-gtk4.ac;
        cgu_config.h.in, mutex.h).

(ryoon)