generate_wrap_init.pl.in: Use g_type_ensure()
generate_wrap_init.pl.in: Use g_type_ensure()

Call g_type_ensure(SomeClass::get_type()).

Redefining the G_GNUC_CONST preprocessor macro does not have the
intended effect (SomeClass::get_type() actually being called) if
the package is compiled and linked with the -flto option.
LTO = link time optimization

https://mail.gnome.org/archives/gtkmm-list/2020-November/msg00009.html

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm