$ opam install dune
The following actions will be performed:
  ∗ install dune 3.10.0

<><> Gathering sources ><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
[dune.3.10.0] found in cache

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
[ERROR] The compilation of dune failed at
        "/data/data/com.termux/files/home/.opam/5.0.0/bin/ocaml boot/bootstrap.ml
        -j 1".

#=== ERROR while compiling dune.3.10.0 ========================================#
# context     2.0.4 | linux/arm64 | ocaml-base-compiler.5.0.0 | https://opam.ocaml.org#b61304c6
# path        ~/.opam/5.0.0/.opam-switch/build/dune.3.10.0
# command     ~/.opam/5.0.0/bin/ocaml boot/bootstrap.ml -j 1
# exit-code   2
# env-file    ~/.opam/log/dune-18226-d2c37b.env
# output-file ~/.opam/log/dune-18226-d2c37b.out
### output ###
# extern value caml_set_oo_id();
# [...]
# /data/data/com.termux/files/home/.opam/5.0.0/lib/ocaml/caml/mlvalues.h:423:18: note: conflicting prototype is here
# CAMLextern value caml_set_oo_id(value obj);
#                  ^
# 2 warnings generated.
# ./.duneboot.exe -j 1
# cd _boot && /data/data/com.termux/files/home/.opam/5.0.0/bin/ocamlopt.opt -o ../_boot/dune.exe -g -I +unix -I +threads unix.cmxa threads.cmxa -no-alias-deps -w -49-6 readdir.c wait3_stubs.c signal_stubs.c platform_stubs.c copyfile_stubs.c dune_digest_stubs.c xdg_stubs.c spawn_stubs.c dune_stats_stubs.c dune_flock.c csexp_rpc_stubs.c fsevents_stubs.c inotify_stubs.c fswatch_win_stubs.c sha512_[...]
# otherlibs/stdune/src/wait3_stubs.c:59:9: error: call to undeclared function 'wait3'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
#   pid = wait3(&status, cv_flags, &ru);
#         ^
# 1 error generated.
#



<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
┌─ The following actions failed
│ λ build dune 3.10.0