Support frustum clipping against z = -1.

Support frustum clipping against z = -1.

This allows performing the depth range adjustment only once as part of the
viewport transform and not have it be affected by transform feedback.

Change-Id: I89fba3b131c234bea064b1b65f50b62261f4c307
Reviewed-on: https://swiftshader-review.googlesource.com/5421
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>