Core 112.06.00 does not build on osx, so constrain it

See janestreet/core#50
Add package atd2cconv 0.0.0
Sync latest compiler pull requests
Merge pull request #3205 from bactrian/sync-prs-1418688001

Sync OCaml compiler PRs
Merge pull request #3204 from smondet/atd2cconv.0.0.0

Add package atd2cconv 0.0.0
Merge pull request #3202 from mirage/core-osx-failure

Core 112.06.00 does not build on osx, so constrain it