Depth format textures can have a comparison operation performed after
their texels have been sampled.

Change-Id: I49f6bb7fab9765265761144ee8b6b62439beb5a3
Reviewed-on: https://swiftshader-review.googlesource.com/5870Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>