Enable libbacktrace support in CI compiled LLVM-backed MacOS builds

[benjaminmordaunt]

I've just installed the 9a80de3 LLVM MacOS nightly build as I wanted backtrace support for the otherwise useless assertion warnings that are received from the numeric_std package.

Unfortunately, even when analysing with -g and using --backtrace-severity=warning on the command-line, I'm still not seeing any backtrace.

Does the CI build use libbacktrace? Is there some way this can be enabled?

[tgingold]

I don't think that libbacktrace works on MacOS.
If you are a MacOS developer, you can try to port a MacOS backtrace system library.

[eine]

In fact, libbactrace is disabled in all CI builds (not only MacOS). See #1578 and ghdl/docker#35.