Nadia.chambers/parallel make 001

[NadiaYvette]

Description

This passes -j flags down from MAKEFLAGS to nix and cabal to speed up builds for me. It also sets ERA=coay and there could be some wanting to change the semantics of how JOBS and NUM_PROCS signal whether to do parallel builds or not. If the Makefile is largely at our group's discretion, it makes sense to just merge the commits instead of carrying them around & cherry-picking them all the time.

Checklist

• [ ] Commit sequence broadly makes sense and commits have useful messages
• [ ] New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
  • integration tests See Runnings tests for more details
• [ ] Any changes are noted in the CHANGELOG.md for affected package
• [ ] The version bounds in .cabal files are updated
• [ ] CI passes. See note on CI. The following CI checks are required:
  • [ ] Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • [ ] Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • [ ] Code builds on Linux, MacOS and Windows for ghc-8.10.7 and ghc-9.2.7
• [ ] Self-reviewed the diff

Note on CI

I don't believe CI uses this for test runs, so it's unlikely to have impacts on it.