compiler: add PERSP to the existing barycentric system values

We need the LINEAR versions for AMD_shader_explicit_vertex_parameter.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3578>
11 files changed