Support metrics for ARM64 servers

[tmcgilchrist]

See patricoferris/ocaml-variorum#5 for support.

[moyodiallo]

It seems the difficulty to generate a static binary using ocaml-varium, is coming from:

• https://github.com/patricoferris/ocaml-variorum/blob/9128770e9df08ca7a90f317acc08b9cd49da6766/src/c/dune#L35
• https://github.com/patricoferris/ocaml-variorum/blob/9128770e9df08ca7a90f317acc08b9cd49da6766/src/c/dune#L32

I'll try to fix it.