[Concurrency] Fix task-to-thread model linking.

[al45tair]

We need to provide some of the additional functions, as stubs, for task-to-thread model.

rdar://141348916

[al45tair]

@swift-ci Please smoke test

[al45tair]

Hopefully we can take this instead of #80194.

[al45tair]

@swift-ci Please smoke test macOS platform

[al45tair]

@swift-ci Please smoke test

[compnerd]

new runtimes side of the changes for the build seem good

[etcwilde]

New runtime build changes look fine to me. I may come back and conditionalize including the platform-specific executors based on the platform to reduce filesystem traffic.

Just the one question on whether we want to include ExecutorImpl.swift in the list of sources where the swift_Concurrency library is declared instead of adding it afterward in each of the executor backend implementations.

[etcwilde]

Is ExecutorImpl.swift going to be used for all executors? If so, it might make sense to include the file wholesale on the main add_library(swift_Concurrency) invocation instead of adding it separately for each executor backend.

[al45tair]

Not necessarily, no. The Embedded Swift build doesn't use ExecutorImpl.swift, currently.

[al45tair]

(I'd like it to, but… there are issues relating to existing users and how they're using it that we need to work out first.)

[al45tair]

@swift-ci Please smoke test macOS platform

[etcwilde]

Build system changes look fine to me

[al45tair]

macOS PR testing timed-out that time.

[al45tair]

@swift-ci Please smoke test macOS

[al45tair]

Now Windows timed out :-(

[al45tair]

@swift-ci Please smoke test Windows platform

[glessard]

@swift-ci Please smoke test macOS

[compnerd]

@swift-ci please test Windows platform

[compnerd]

@swift-ci please smoke test macOS platform

[glessard]

lib/swift/shims/module.modulemap:1:8: error: redefinition of module 'SwiftShims'
 1 | module SwiftShims {
   |        `- error: redefinition of module 'SwiftShims'
 2 |   header "AssertionReporting.h"
 3 |   header "CoreFoundationShims.h"

...

/lib/swift/shims/module.modulemap:28:8: error: redefinition of module '_SwiftConcurrencyShims'
26 | }
27 | 
28 | module _SwiftConcurrencyShims {
   |        `- error: redefinition of module '_SwiftConcurrencyShims'
29 |   header "_SwiftConcurrency.h"
30 | }

[compnerd]

I'm going to split out some of the build changes to get the CI unblocked.

[compnerd]

Seems that attempt crashes the compiler - fortunately @glessard did put up a revert for the issue. I've triggered the auto-merge to get CI healthy again.