Accept mismatching auxiliary interpolations. The ES3.1 spec, and discussion on Khronos.org, confirm that dEQP is correct in accepting mismatching centroid specifiers in shader linkage. Mismatching flat/smooth is still a link error. Fixes: shaders.linkage.varying.rules.differing_interpolation_2 Change-Id: I3016f4147e7c1b16b02371ee95866c8daf826212 Reviewed-on: https://chromium-review.googlesource.com/251205 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>