Can't build with clang

[CodingCanuck]

Per #73 (comment) , eventuals-grpc currently doesn't compile under clang (because the version of abseil we pin to doesn't compile under clang).

Super non-urgent, but it would be nice if this compiled under clang (if only because clang might offer faster compile times: see #73 )

[CodingCanuck]

@while-false FYI

[benh]

FYI, I definitely use clang to build eventuals-grpc almost daily! And the macos-latest GitHub Workflow build also uses clang. Of course, these are both on macOS, not Linux.

[CodingCanuck]

Per my monologue on #73 (comment) , the newest gRPC release 1.44.0 doesn't compile for us due to a breaking change introduced in grpc 1.42.0: https://github.com/grpc/grpc/pull/27507/files/ca4a1d7346f854fe97b5e5fd2702f60ed5dbe45a#r807384888

The author just merged in a probable fix: grpc/grpc#28933

And I just created a minimal repro for them: https://github.com/CodingCanuck/grpc-build-error-1-42-rules_python.patch which they can hopefully use to verify their fix