This allows Chromium to use the SwiftShader Vulkan library
with the Subzero backend when available.

Bug: chromium:1060139
Change-Id: I444b3e6844c52781ada9f51c8ddb4e4d2ea6a6d4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/42108
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>