rmlbuild not compatible with ocaml 5
Uses Pervasives:
```
\#=== ERROR while compiling rmlbuild.0.14.0-00 =================================#
\# context 2.2.0~alpha3~dev | linux/x86_64 | ocaml-base-compiler.5.1.0 | file:///home/opam/opam-repository
\# path ~/.opam/5.1/.opam-switch/build/rmlbuild.0.14.0-00
\# command ~/.opam/opam-init/hooks/sandbox.sh build make check-if-preinstalled all opam-install
\# exit-code 2
\# env-file ~/.opam/log/rmlbuild-7-0923b3.env
\# output-file ~/.opam/log/rmlbuild-7-0923b3.out
\### output ###
\# if test -d /home/opam/.opam/5.1/lib/ocaml/rmlbuild; then\
\# >&2 echo "ERROR: Preinstalled rmlbuild detected at"\
\# "/home/opam/.opam/5.1/lib/ocaml/rmlbuild";\
\# >&2 echo "Installation aborted; if you want to bypass this"\
\# "safety check, pass CHECK_IF_PREINSTALLED=false to make";\
\# exit 2;\
\# fi
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/const.ml
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/loc.mli
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/loc.ml
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/discard_printf.mli
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/discard_printf.ml
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/signatures.mli
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/my_std.mli
\# ocamlc.opt -w L -w R -w Z -I src -I +unix -safe-string -bin-annot -strict-sequence -c src/my_std.ml
\# File "src/my_std.ml", line 127, characters 20-38:
\# 127 | let compare = Pervasives.compare
\# ^^^^^^^^^^^^^^^^^^
\# Error: Unbound module Pervasives
\# make: *** [Makefile:423: src/my_std.cmo] Error 2
```
Signed-off-by: Marcello Seri <marcello.seri@gmail.com>