By default the build script will enable native-comp if it detects it in
the source tree. This caused recently nightly builds of master to be
built without native-comp due to recent changes in Emacs' configure
script which broke native-comp detection. More details here:
https://github.com/jimeh/build-emacs-for-macos/issues/76
Hence we explicitly enable native-comp now for the nightly master and
emacs-28 builds, which will cause the build script to fail if it cannot
detect native-comp support in the source tree.
Any failure to detect native-comp in master and emacs-28 branches would
at this point be due to a bug/issue with the build script, rather than
Emacs' source tree.
The macos-10.15 runner is now deprecated and no longer usable. Hence all
GitHub Actions workflows using a macOS runner need to upgraded to
macos-11.
As far as I know, this will have a knock-on effect of causing Emacs
builds to require macOS 11.x (Big Sur) or later from now on.
This makes the workflow setup more flexible, and less copy/pasting
between workflows. And also makes the process of adding nightly builds
for non-master branches easier too.
