nir: add fceil lowering

lowers ceil(x) as -floor(-x)

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>

src/compiler/nir/nir.h

@@ -2130,6 +2130,9 @@ typedef struct nir_shader_compiler_options {
    /** lowers ffract to fsub+ffloor: */
    bool lower_ffract;
 
+   /** lowers fceil to fneg+ffloor+fneg: */
+   bool lower_fceil;
+
    bool lower_ldexp;
 
    bool lower_pack_half_2x16;