You do not need a tool. Just write a script in your favorite scripting language to format your glade file as a string literal C:
, glade_file.c:
const gchar *my_glade_file =
"<interface>"
"<object class=\"GtkDialog\">"
"<et-cetera />"
"</object>"
"</interface>";
glade_file.c , :
extern const gchar *my_glade_file;
result = gtk_builder_add_from_string(builder, my_glade_file, -1, &error);