Install linux-headers package in Alpine build for bechamel package

[shakthimaan]

The bechamel package CI is failing for Alpine 3.19 as observed in the logs at:
https://ocaml.ci.dev/github/mirage/bechamel/commit/a54a0b47300ed4ae9b95d4b05af701012caa31ca

The fix is to install the linux-header package using apk before proceeding to install the package dependencies.

I see there is dev_packages as an extra argument to module Apk in linux.ml:

 let dev_packages ?extra () =
    install
      "build-base patch tar ca-certificates git rsync curl sudo bash \
       libx11-dev nano coreutils xz ncurses-dev%s"
      (match extra with None -> "" | Some x -> " " ^ x)

See https://github.com/ocurrent/ocaml-dockerfile/blob/master/src-opam/linux.ml#L138

Is there a way to pass these dev_packages list from the respective project sources directory, say from https://github.com/mirage/bechamel?

[benmandrew]

System package dependencies should be specified in the .opam file with the conf- opam packages. It looks like the conf-linux-libev-dev package to me (https://opam.ocaml.org/packages/conf-linux-libc-dev/).