Xija/Ska.Numpy build fail on Github Mac OS environment

[javierggt]

Conda package build fails on Github Mac OS environment. See this run.

I believe the relevant error is:

ld: unsupported tapi file type '!tapi-tbd' in YAML file '/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/lib/libSystem.tbd' for architecture x86_64
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
error: command 'x86_64-apple-darwin13.4.0-clang' failed with exit status 1

A release 4.21.1 was successfully built, while it now fails to build using a similar workflow. For this reason, we believe this is due to changes in the environment.

We figured it might have to do with this issue, but a test workflow applying the mitigation proposed there to choose xcode did not succeed.

[javierggt]

To expedite the current release, I did the following:

• built the package on my Mac, which should be OK,
• uploaded it to ska3-conda/masters
• modified the build workflow in sot/test-actions to disable Mac builds
• triggered this workflow, which uploads linux/win packages and re-indexes

[javierggt]

I have verified that the build currently fails in my own machine using XCode 12.4. I also did a brute-force test to see which versions are ok, and this is the result:

+------+--------+
| 10.3 | not OK |
| 11.2 |     OK |
| 11.3 |     OK |
| 11.4 |     OK |
| 11.5 |     OK |
| 11.7 |     OK |
| 12.  |     OK |
| 12.2 | not OK |
| 12.3 | not OK |
| 12.4 | not OK |
+------+--------+

It seems we can fix our automated builds by requiring XCode 12 or older, but as things move forward we should check what are the issues in newer XCode versions.

[javierggt]

Commits cb1e6b2 and 41a5f91 fix this issue as can be seen in this build.

I am making similar commits in Ska.Numpy and cxotime.