This is a pure move with no changes.

The goal here is to centralize the concurrent synchronization primitives, and not have them scattered around the codebase.

Bug: b/133127573
Change-Id: I6abdfc34bf13ce455983610ff0c686778e0e9e4c
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31677
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <headlessclayton@gmail.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>