ir_to_mesa: Implement ir_unop_any using DP4 w/saturate or DP4 w/SLT

ir_to_mesa: Implement ir_unop_any using DP4 w/saturate or DP4 w/SLT

This is just like the ir_binop_logic_or case.  The operation
ir_unop_any is (a.x || a.y || a.z || a.w).  Logical-or is implemented
using addition (followed by clampling to [0,1]) on values of 0.0 and
1.0.  Replacing the logical-or operators with addition gives (a.x +
a.y + a.z + a.w).  This can be implemented using a dot-product with a
vector of all 1.0.

Previously a SNE instruction was used to clamp the resulting logic
value to [0,1].  In a fragment shader, using a saturate on the
dot-product has the same effect.  Adding the saturate to the
dot-product is free, so (at least) one instruction is saved.

In a vertex shader, using an SLT on the negation of the dot-product
result has the same effect.  Many older shader architectures do not
support the SNE instruction.  It must be emulated using two SLT
instructions and an ADD.  On these architectures, the single SLT saves
two instructions.

Reviewed-by: Eric Anholt <eric@anholt.net>