gitypelib: Switch to refcounting

Since `GITypelib` is exposed in the public libgirepository API, it needs
to be a boxed type. So we either need to add a `copy` method to mirror
the existing `free` method, or switch to refcounting. The latter option
seems better, since a `GITypelib` contains internal state about open
`GModule`s and the semantics for copying that would be potentially
complex.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3155

girepository/compiler/compiler.c

@@ -218,7 +218,7 @@ main (int argc, char **argv)
   g_debug ("[building] start");
 
   {
-    GITypelib *typelib;
+    GITypelib *typelib = NULL;
 
     if (shlibs)
       {
@@ -238,8 +238,8 @@ main (int argc, char **argv)
 
     if (!write_out_typelib (NULL, typelib))
       return 1;
-    gi_typelib_free (typelib);
-    typelib = NULL;
+
+    g_clear_pointer (&typelib, gi_typelib_unref);
   }
 
   g_debug ("[building] done");