- Add variants for various common build flags, including support for both versions of the Racket VM environment.
- Prevent `-j` flags to `make`, which has been known to cause problems with Racket builds.
- Prefer the minimal release to improve install times. Bells and whistles carry their own runtime dependencies and should be installed via `raco`. An enterprising user may even create a `RacketPackage` class to make spack aware of `raco` installed packages.
- Match the official version numbering scheme.
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