Custom main and global executors work hasn't passed Swift Evolution yet,
so we need to avoid leaking it as API until it does.
To that end, underscore all the things.
rdar://151147606
If you use SwiftStdlibCurrentOS availability, you will be able to
use new types and functions from within the implementation. This
works by, when appropriate, building with the CurrentOS availability
set to the current deployment target.
rdar://150944675
Reorganise the Concurrency code so that it's possible to completely
implement executors (both main and global) in Swift.
Provide API to choose the desired executors for your application.
Also make `Task.Sleep` wait using the current executor, not the global
executor, and expose APIs on `Clock` to allow for conversion between
time bases.
rdar://141348916
We have been only including a subset of files and functionality on Embedded Concurrency, let's instead include all the
source files, and have a fine grained opt out on things that don't yet work. Namely, this is still avoiding clocks, task
sleeping and custom executors.
Add a test for AsyncStream and continuations on Embedded Concurrency.
The `_SwiftConcurrencyShims` module was imported `@_implementationOnly` which
was causing warnings to be emitted during the stdlib build. The module
currently serves no purpose; the only declaration it contains is a defunct
`_SwiftContext` struct which is not referenced by anything. The module needs to
continue to exist for source compatibility, though, since it is part of the
toolchain and imported publicly from other modules.
