Do not build mrmime.0.1.0 on OCaml 5
FTBFS due to a multiple of reasons: `Obj.extension_id` removal,
`Pervasives`:
#=== ERROR while compiling mrmime.0.1.0 =======================================#
# context 2.2.0~alpha~dev | linux/x86_64 | ocaml-base-compiler.5.0.0 | file:///home/opam/opam-repository
# path ~/.opam/5.0/.opam-switch/build/mrmime.0.1.0
# command ~/.opam/opam-init/hooks/sandbox.sh build dune build -p mrmime -j 71
# exit-code 1
# env-file ~/.opam/log/mrmime-8-8626ab.env
# output-file ~/.opam/log/mrmime-8-8626ab.out
### output ###
# (cd _build/default && /home/opam/.opam/5.0/bin/ocamlc.opt -w -40 -w -32-27 -g -bin-annot -I lib/.mrmime.objs/byte -I /home/opam/.opam/5.0/lib/angstrom -I /home/opam/.opam/5.0/lib/base64 -I /home/opam/.opam/5.0/lib/base64/rfc2045 -I /home/opam/.opam/5.0/lib/bigstringaf -I /home/opam/.opam/5.0/lib/bytes -I /home/opam/.opam/5.0/lib/coin -I /home/opam/.opam/5.0/lib/domain-name -I /home/opam/.opam/5.0/lib/fmt -I /home/opam/.opam/5.0/lib/ipaddr -I /home/opam/.opam/5.0/lib/ke -I /home/opam/.opam/5.0/lib/macaddr -I /home/opam/.opam/5.0/lib/pecu -I /home/opam/.opam/5.0/lib/ptime -I /home/opam/.opam/5.0/lib/rosetta -I /home/opam/.opam/5.0/lib/rresult -I /home/opam/.opam/5.0/lib/uutf -I /home/opam/.opam/5.0/lib/uuuu -I /home/opam/.opam/5.0/lib/yuscii -I lib/butils/.butils.objs/byte -I lib/encoder/.encoder.objs/byte -intf-suffix .ml -no-alias-deps -open Mrmime__ -o lib/.mrmime.objs/byte/mrmime__Extension.cmo -c -impl lib/extension.ml)
# File "lib/extension.ml", line 21, characters 9-25:
# 21 | (Obj.extension_id [%extension_constructor T])
# ^^^^^^^^^^^^^^^^
# Error: Unbound value Obj.extension_id
# File "lib/encoded_word.ml", line 91, characters 25-41:
# 91 | let equal_charset a b = (Pervasives.( = ) : charset -> charset -> bool) a b
# ^^^^^^^^^^^^^^^^
# Error: Unbound module Pervasives
# File "lib/extension.ml", line 21, characters 9-25:
# 21 | (Obj.extension_id [%extension_constructor T])
# ^^^^^^^^^^^^^^^^
# Error: Unbound value Obj.extension_id
# File "lib/encoded_word.ml", line 91, characters 25-41:
# 91 | let equal_charset a b = (Pervasives.( = ) : charset -> charset -> bool) a b
# ^^^^^^^^^^^^^^^^
# Error: Unbound module Pervasives
(Deprecation warnings from Fmt removed from output since these are not
causing failures)