Add support for OCaml 5.4

[kit-ty-kate]

Fixes the following error:

#=== ERROR while compiling ppx_deriving.6.1.0 =================================#
# context              2.4.0~alpha2 | linux/x86_64 | ocaml-base-compiler.5.4.0~alpha1 | file:///home/opam/opam-repository
# path                 ~/.opam/5.4/.opam-switch/build/ppx_deriving.6.1.0
# command              ~/.opam/5.4/bin/dune build -p ppx_deriving -j 1
# exit-code            1
# env-file             ~/.opam/log/ppx_deriving-14-63972d.env
# output-file          ~/.opam/log/ppx_deriving-14-63972d.out
### output ###
# (cd _build/default && /home/opam/.opam/5.4/bin/ocamlopt.opt -w -40 -w -27-9 -g -I src/api/.ppx_deriving_api.objs/byte -I src/api/.ppx_deriving_api.objs/native -I /home/opam/.opam/5.4/lib/ocaml-compiler-libs/common -I /home/opam/.opam/5.4/lib/ocaml-compiler-libs/shadow -I /home/opam/.opam/5.4/lib/ocaml/compiler-libs -I /home/opam/.opam/5.4/lib/ppx_derivers -I /home/opam/.opam/5.4/lib/ppxlib -I /home/opam/.opam/5.4/lib/ppxlib/ast -I /home/opam/.opam/5.4/lib/ppxlib/astlib -I /home/opam/.opam/5.4/lib/ppxlib/print_diff -I /home/opam/.opam/5.4/lib/ppxlib/stdppx -I /home/opam/.opam/5.4/lib/ppxlib/traverse_builtins -I /home/opam/.opam/5.4/lib/sexplib0 -I /home/opam/.opam/5.4/lib/stdlib-shims -intf-suffix .ml -no-alias-deps -o src/api/.ppx_deriving_api.objs/native/ppx_deriving.cmx -c -impl src/api/ppx_deriving.pp.ml)
# File "ppx_deriving.cppo.ml", line 352, characters 54-57:
# Error: The value lid has type Ppxlib.longident = Astlib.Longident.t
#        but an expression was expected of type
#          Ocaml_common.Longident.t = Longident.t
# (cd _build/default && /home/opam/.opam/5.4/bin/ocamlc.opt -w -40 -w -27-9 -g -bin-annot -bin-annot-occurrences -I src/api/.ppx_deriving_api.objs/byte -I /home/opam/.opam/5.4/lib/ocaml-compiler-libs/common -I /home/opam/.opam/5.4/lib/ocaml-compiler-libs/shadow -I /home/opam/.opam/5.4/lib/ocaml/compiler-libs -I /home/opam/.opam/5.4/lib/ppx_derivers -I /home/opam/.opam/5.4/lib/ppxlib -I /home/opam/.opam/5.4/lib/ppxlib/ast -I /home/opam/.opam/5.4/lib/ppxlib/astlib -I /home/opam/.opam/5.4/lib/ppxlib/print_diff -I /home/opam/.opam/5.4/lib/ppxlib/stdppx -I /home/opam/.opam/5.4/lib/ppxlib/traverse_builtins -I /home/opam/.opam/5.4/lib/sexplib0 -I /home/opam/.opam/5.4/lib/stdlib-shims -intf-suffix .ml -no-alias-deps -o src/api/.ppx_deriving_api.objs/byte/ppx_deriving.cmo -c -impl src/api/ppx_deriving.pp.ml)
# File "ppx_deriving.cppo.ml", line 352, characters 54-57:
# Error: The value lid has type Ppxlib.longident = Astlib.Longident.t
#        but an expression was expected of type
#          Ocaml_common.Longident.t = Longident.t

[gasche]

Fair enough, thanks!