Use the `%target-swift-5.1-abi-triple` substitution to compile the tests for
deployment to the minimum OS versions required for use of _Concurrency APIs,
instead of disabling availability checking.
Adding test to verify correct behavior from swift when targeting arm64
macOS. We caught the fact that the optimizer got smarter on arm64 in the
watchOS test, which doesn't seem to get run in PR testing. The updated
test catches it now.
When we deploy to a minimum target that is not known to support extended
frame information the function prolog of Swift async functions will
contain a reference to swift_async_extendedFramePointerFlags. This
reference needs to be weak like any async symbols.
rdar://83412550
control swift extended frame information emission
On linux we default to disable the extended frame info (since the system
libraries don't support it).
On darwin the default is to automatically choose based on the deployment target.
The Concurrency library explicitly forces extended frame information and the
back deployment library explicitly disables it.
