Yay compatibility and predictability!

It’s the magic sentence that allows pods dependent on RxLibrary to be
archived correctly by XCode.

It’s less than ideal, and seems arbitrary (why RxLibrary specifically?),
so we’ll try to produce a minimal case and open an issue with it in the
Cocoapods repo.

Pending:

- Tag BoringSSL repo.
- Tag gRPC repo.
- Build the plugin, zip it, and add it to the release.
- Push Cocoapods to trunk.

Rename async_execution_lock --> combiner, make it use closures, unroll previous changes for idleness

This reverts commit d88e15ce.

files

This reverts commit 48d833a9, reversing
changes made to 66e9d8e8.