BUG/MEDIUM: threads: Disable the workaround to load libgcc_s on macOS

BUG/MEDIUM: threads: Disable the workaround to load libgcc_s on macOS

Don't use the workaround to load libgcc_s on macOS. It is not needed
there, and it causes issues, as recent macOS dislike processes that fork
after threads where created (and the workaround creates a temporary
thread). This fixes crashes on macOS at least when using master-worker,
and using the system resolver.

This should fix Github issue #3035

This should be backported up to 2.8.