Bisected to:
mesa c1eedb43f32f6a3733f26e7918eb028f68bd60a4
Author:     Ville Syrjälä <ville.syrjala@linux.intel.com>

i915: Fix wpos_tex vs. -1 comparison

wpos_tex used to be a GLuint so assigning -1 to it and
later comparing with -1 worked correctly, but commit
c349031c27b7 ("i915: Fix texcoord vs. varying collision in
fragment programs") changed wpos_tex to uint8_t and hence
broke the comparison. To fix this define a more explicit
invalid value for wpos_tex.

Failing tests:
ES2-CTS.functional.clipping.polygon.multiple_0
ES2-CTS.functional.clipping.polygon.multiple_0_viewport_center
ES2-CTS.functional.clipping.polygon.multiple_0_viewport_corner
ES2-CTS.functional.clipping.polygon.multiple_1
ES2-CTS.functional.clipping.polygon.multiple_1_viewport_center
ES2-CTS.functional.clipping.polygon.multiple_1_viewport_corner
ES2-CTS.functional.clipping.polygon.poly_attrib_clip
ES2-CTS.functional.clipping.polygon.poly_attrib_clip_viewport_center
ES2-CTS.functional.clipping.polygon.poly_attrib_clip_viewport_corner
ES2-CTS.functional.rasterization.interpolation.projected.line_loop
ES2-CTS.functional.rasterization.interpolation.projected.line_strip
ES2-CTS.functional.rasterization.interpolation.projected.lines
ES2-CTS.functional.rasterization.interpolation.projected.triangle_fan
ES2-CTS.functional.rasterization.interpolation.projected.triangle_strip
ES2-CTS.functional.rasterization.interpolation.projected.triangles
ES2-CTS.functional.clipping.polygon.multiple_1
Standard Output:

Render target size: 400x300
Viewport: left=0	bottom=0	width=200	height=200
Rendering triangles. Coordinates:
	v0 (x=-0.2	y=-0.3	z=0	w=1)		(red)
	v1 (x=0.2	y=-0.3	z=0	w=1)		(yellow)
	v2 (x=0	y=-0.9	z=2	w=1)		(+Z clip)	(blue)
	v0 (x=0.6	y=1.2	z=0	w=1)		(+Y clip)	(red)
	v1 (x=1.2	y=0.6	z=0	w=1)		(+X clip)	(yellow)
	v2 (x=0.6	y=0.6	z=0	w=1)		(blue)
	v0 (x=0.6	y=-1.2	z=0	w=1)		(-Y clip)	(red)
	v1 (x=1.2	y=-0.6	z=0	w=1)		(+X clip)	(yellow)
	v2 (x=9.6	y=-9.6	z=0	w=16)		(blue)
	v0 (x=0.6	y=1.2	z=0	w=1)		(+Y clip)	(red)
	v1 (x=1.2	y=0.6	z=0	w=1)		(+X clip)	(yellow)
	v2 (x=9.6	y=9.6	z=0	w=16)		(blue)
	v0 (x=-0.6	y=1.2	z=0	w=1)		(+Y clip)	(red)
	v1 (x=-1.2	y=0.6	z=0	w=1)		(-X clip)	(yellow)
	v2 (x=-9.6	y=9.6	z=0	w=16)		(blue)
	v0 (x=-0.6	y=-1.2	z=0	w=1)		(-Y clip)	(red)
	v1 (x=-1.2	y=-0.6	z=0	w=1)		(-X clip)	(yellow)
	v2 (x=-9.6	y=-9.6	z=0	w=16)		(blue)
Comparing images... 
Deviation within radius of 1 is allowed.
6 faulty pixels are allowed.
80 deviating pixel(s) found.
4588 faulty pixel(s) found.
Got 4588 faulty pixel(s).


Sample output:
ES2-CTS.functional.clipping.polygon.multiple_1
Standard Output:

Render target size: 400x300
Viewport: left=0	bottom=0	width=200	height=200
Rendering triangles. Coordinates:
	v0 (x=-0.2	y=-0.3	z=0	w=1)		(red)
	v1 (x=0.2	y=-0.3	z=0	w=1)		(yellow)
	v2 (x=0	y=-0.9	z=2	w=1)		(+Z clip)	(blue)
	v0 (x=0.6	y=1.2	z=0	w=1)		(+Y clip)	(red)
	v1 (x=1.2	y=0.6	z=0	w=1)		(+X clip)	(yellow)
	v2 (x=0.6	y=0.6	z=0	w=1)		(blue)
	v0 (x=0.6	y=-1.2	z=0	w=1)		(-Y clip)	(red)
	v1 (x=1.2	y=-0.6	z=0	w=1)		(+X clip)	(yellow)
	v2 (x=9.6	y=-9.6	z=0	w=16)		(blue)
	v0 (x=0.6	y=1.2	z=0	w=1)		(+Y clip)	(red)
	v1 (x=1.2	y=0.6	z=0	w=1)		(+X clip)	(yellow)
	v2 (x=9.6	y=9.6	z=0	w=16)		(blue)
	v0 (x=-0.6	y=1.2	z=0	w=1)		(+Y clip)	(red)
	v1 (x=-1.2	y=0.6	z=0	w=1)		(-X clip)	(yellow)
	v2 (x=-9.6	y=9.6	z=0	w=16)		(blue)
	v0 (x=-0.6	y=-1.2	z=0	w=1)		(-Y clip)	(red)
	v1 (x=-1.2	y=-0.6	z=0	w=1)		(-X clip)	(yellow)
	v2 (x=-9.6	y=-9.6	z=0	w=16)		(blue)
Comparing images... 
Deviation within radius of 1 is allowed.
6 faulty pixels are allowed.
80 deviating pixel(s) found.
4588 faulty pixel(s) found.
Got 4588 faulty pixel(s).