About non-macOS systems that use Darwin kernel

[673123]

Output of brew config

N/A

Output of brew doctor

N/A

Description of issue

There exist usable Darwin systems that are not macOS. For example: https://github.com/darlinghq/darling. However, Homebrew currently detects if it's macOS only through kernel type. Then if someone tries to run Homebrew on Darling, they will encounter strange issues instead of message telling them their platform is not supported.

[p-linnane]

Homebrew targets macOS and Linux. Darling is an unsupported platform. We'd consider a PR that adds better detection if someone actually hits this, but we're not going to proactively work on it. Thanks for raising it though.