Switching SwiftShader on ChromeOS from LLVM to Subzero.

Change-Id: Ica9ac278272f99b94d365f03fbd7a4860ad3503d
Reviewed-on: https://swiftshader-review.googlesource.com/11309Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>