Outdated `src/.depend` file in 2.18.12 release tarball

[trofi]

The src/.depend file included in latest release is outdated and does not contain a dependency of 'gtkThInit.cmo' on 'gtkThread.cmi'.

As a result build on make --shuffle (added in https://savannah.gnu.org/bugs/index.php?62100) fails in about 50% cases as:

make -C src world
make[1]: Entering directory '/build/source/src'
ocamlc.opt   -w s-3+52 -c  gtkThInit.ml
File "gtkThInit.ml", line 27, characters 13-28:
27 | let thread = GtkThread.start ()
                  ^^^^^^^^^^^^^^^
Error: Unbound module GtkThread
make[1]: *** [Makefile:193: gtkThInit.cmo] Error 2 shuffle=1656165991
make[1]: Leaving directory '/build/source/src'
make: *** [Makefile:5: world] Error 2 shuffle=1656165991

If I run make depend against ocaml-4.13 I see expected depend:

$ ./configure
$ make depend
$ cat src/.depend
...
gtkThInit.cmo : \
    gtkThread.cmi
...

[garrigue]

Done in 91ce823475