nir/lower_double_ops: lower mod()

There are rounding errors with the division in i965 that affect
the mod(x,y) result when x = N * y. Instead of returning '0' it
was returning 'y'.

This lowering pass fixes those cases.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/compiler/nir/nir.h

@@ -2425,7 +2425,8 @@ typedef enum {
    nir_lower_dfloor = (1 << 4),
    nir_lower_dceil = (1 << 5),
    nir_lower_dfract = (1 << 6),
-   nir_lower_dround_even = (1 << 7)
+   nir_lower_dround_even = (1 << 7),
+   nir_lower_dmod = (1 << 8)
 } nir_lower_doubles_options;
 
 void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options options);