10.15 Xcode version: Buildbot, vs. GitHub CI

[Christopher Chavez]

> This brings up two questions:
> * Would it be feasible to update our 10.15 buildbot to a newer Xcode release? Or are there certain ports/situations that necessitate remaining with 11.7?

Xcode 12 prohibiting implicit function declarations is probably no longer a reason since these must have been resolved to support Big Sur/Monterey.

> * Do we have control over the Xcode version used for GitHub CI, or is 12.4 the only option?

Yes, or I thought we did. A year ago I tried adding a second 10.15 CI builder to have both Xcode 11 and Xcode 12 beta: https://github.com/macports/macports-ports/pull/8162

The important part was to run xcode-select with the path for the desired version. The available versions are listed at https://github.com/actions/virtual-environments/blob/main/images/macos/macos-10.15-Readme.md#xcode

However there may have been an issue where the command line tools didn’t match the selected Xcode version.

Christopher A. Chavez