Write the shaders so that texcoord's register index in the vertex output
signature matches the register index in the pixel input signature
(o0 and v0 in this case) in SM4.
point-sprite.shader_test is not technically well formed since, in SM4,
the vertex output signature should be:
// Output signature:
// Name Index Mask Register SysValue Format Used
// -------------------- ----- ------ -------- -------- ------- ------
// sv_position 0 xyzw 0 POS float xyzw
// texcoord 0 xy 1 NONE float xy
and the pixel input signature should be:
// Input signature:
// Name Index Mask Register SysValue Format Used
// -------------------- ----- ------ -------- -------- ------- ------
// texcoord 0 xy 0 NONE float xy
so we are not passing "texcoord" properly to the pixel shader, even on
Windows.
