varcc.ml fails to build with OCaml 5

[olafhering]

[   39s] + make world
[   39s] make -C src world
[   39s] make[1]: Entering directory '/home/abuild/rpmbuild/BUILD/ocaml-lablgtk2-2.18.12/src'
[   39s] ocamlc.opt   -w s-3+52 -c  varcc.ml
[   39s] File "varcc.ml", line 26, characters 27-41:
[   39s] 26 |         Buffer.add_char b (Char.lowercase id.[i])
[   39s]                                 ^^^^^^^^^^^^^^
[   39s] Error: Unbound value Char.lowercase
[   39s] make[1]: *** [Makefile:193: varcc.cmo] Error 2

[garrigue]

Fixed by 9cdf1d7