This corresponds to the VK_FUCHSIA_external_semaphore extension
which uses a Zircon event object to communicate across processes.

Bug: b/140421726
Change-Id: I47b235d4ff7d787491738422bda6fdf853803ab7
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35969
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: David Turner <digit@google.com>