provide default values of `.h.in` files to be able to build without running meson, etc
those would be
/gmodule/gmoduleconf.h.in
/glib/gnulib/gnulib_math.h.in
/glib/glibconfig.h.in
/gio/gnetworking.h.in
those would be
/gmodule/gmoduleconf.h.in
/glib/gnulib/gnulib_math.h.in
/glib/glibconfig.h.in
/gio/gnetworking.h.in