The repo at https://github.com/ARMmbed/homebrew-formulae seems to no longer be maintained – recent pull requests for the latest versions have been ignored. It would be great if this repo could be opened up to more collaborators, pull requests accepted, or otherwise closed as alternatives exist.
I’m the maintainer of the alternative osx-cross/homebrew-arm – I’ll merge the gcc 10 pr soon.
Let me know if you have any questions.
EDIT: the PR has been merge, GCC 10 is available