gallivm/tessellator: use private functions for min/max to avoid namespace issues

gallivm/tessellator: use private functions for min/max to avoid namespace issues

Different builds are failing because of namespace collisions here.

Just fix the MS code to avoid it.

Fixes: bd0188f9eab ("gallium/auxiliary: add the microsoft tessellator and a pipe wrapper.")
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2586
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4016>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4016>