This patch automates maintaining the right compatibility override
section names so we don't need to remember to update them by hand with
each version.
The expansions look like
'"__swift" "5" "9" "_hooks"' and
'"__s" "5" "9" "async_hook"'.
Note: The section names can only grow to be 16 characters long. If we
see explosions regarding these names, that could be why.
We were detaching the child by just modifying the list, but the cancellation path was assuming that that would not be done without holding the task status lock.
This patch just fixes the current runtime; the back-deployment side is complicated.
Fixes rdar://88398824
Take the existing CompatibilityOverride mechanism and generalize it so it can be used in both the runtime and Concurrency libraries. The mechanism is preprocessor-heavy, so this requires some tricks. Use the SWIFT_TARGET_LIBRARY_NAME define to distinguish the libraries, and use a different .def file and mach-o section name accordingly.
We want the global/main executor functions to be a little more flexible. Instead of using the override mechanism, we expose function pointers that can be set by the compatibility library, or by any other code that wants to use a custom implementation.
rdar://73726764
