The Python build system always enables concurrency, but CMake has it
disable by default. Collaborators that do not use the Python build
system and use directly CMake will have it disable, unless they
explicitely enable it. If the tests are not marked as requiring the
concurrency features, the tests will fail to execute when concurrency is
disabled.
The changes add the `REQUIRES: concurrency` line to many tests that deal
with concurrency, but wasn't marked as such.
Previously, when lowering the entry point of an async function, the
parameters were lowered to explosions that matched those of sync
functions, namely native explosions. That is incorrect for async
functions where the structured values are within the async context.
Here, that error is fixed, by adding a new customization point to
NativeCCEntryPointArgumentEmission which behaves as before for sync
functions but which simply extracts an argument from the async context
for async functions.
rdar://problem/71260972
