i915: Fix gl_Fragcoord interpolation

i915: Fix gl_Fragcoord interpolation

gl_FragCoord contains the window coordinates so it seems to me that
we should not use perspective correct interpolation for it. At least
now I get similar output as i965/swrast/llvmpipe produce.

This fixes dEQP-GLES2.functional.shaders.builtin_variable.fragcoord_w.
dEQP-GLES2.functional.shaders.builtin_variable.fragcoord_xyz was already
passing, though I'm not quite sure how it managed to do that.

v2: Add definitons for the S3 "wrap shortest" bits as well (Ian)

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>