Instead, 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.
Specifically, I am transforming it from "may cause a race" -> "may cause a data
race". Adding data is a small thing, but it adds a bunch of nice clarity.
I fixed a bunch of small issues around here that resulted in a bunch of radars
being fixed. Specifically:
1. I made it so that we treat function_refs that are from an actor isolated
function as actor isolated instead of sendable.
2. I made it so that autoclosures which return global actor isolated functions
are treated as producing a global actor isolated function.
3. I made it so that we properly handle SILGen code patterns produced by
Sendable GlobalActor isolated things.
rdar://125452372
rdar://121954871
rdar://121955895
rdar://122692698
