GNU make job server-alike for GHC --make

Motivation

A problem when building large amounts of dependencies with stack or cabal is that we don't get to exploit any module level parallelism due to cabal using --make mode without any -j flags. It is sensible to not pass any -j: cabal-install uses the parallelism between packages too so it isn't easy choosing how many threads to allow.

Proposal

Have some feature like the GNU make jobserver in GHC.

GNU make documentation: https://www.gnu.org/software/make/manual/html_node/Job-Slots.html

Notes

rust's cargo is both a jobserver client and a jobserver server since https://github.com/rust-lang/cargo/pull/4110

Ocaml decided the jobserver protocol was too hairy: https://github.com/ocaml/dune/pull/4331