compiler/spirv: set is_shadow for depth comparitor sampling opcodes

From the SPIR-V spec, OpTypeImage:

"Depth is whether or not this image is a depth image. (Note that
 whether or not depth comparisons are actually done is a property of
 the sampling opcode, not of this type declaration.)"

The sampling opcodes that specify depth comparisons are
OpImageSample{Proj}Dref{Explicit,Implicit}Lod, so we should set
is_shadow only for these (we were using the deph property of the
image until now).

v2:
 - Do the same for OpImageDrefGather.
 - Set is_shadow to false if the sampling opcode is not one of these (Jason)
 - Reuse an existing switch statement instead of adding a new one (Jason)

Fixes crashes in:
dEQP-VK.spirv_assembly.instruction.graphics.image_sampler.depth_property.*

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Cc: mesa-stable@lists.freedesktop.org

src/compiler/spirv/spirv_to_nir.c

@@ -1908,7 +1908,6 @@ vtn_handle_texture(struct vtn_builder *b, SpvOp opcode,
    const struct glsl_type *image_type = sampled.type->type;
    const enum glsl_sampler_dim sampler_dim = glsl_get_sampler_dim(image_type);
    const bool is_array = glsl_sampler_type_is_array(image_type);
-   const bool is_shadow = glsl_sampler_type_is_shadow(image_type);
 
    /* Figure out the base texture operation */
    nir_texop texop;
@@ -2032,6 +2031,7 @@ vtn_handle_texture(struct vtn_builder *b, SpvOp opcode,
       break;
    }
 
+   bool is_shadow = false;
    unsigned gather_component = 0;
    switch (opcode) {
    case SpvOpImageSampleDrefImplicitLod:
@@ -2040,6 +2040,7 @@ vtn_handle_texture(struct vtn_builder *b, SpvOp opcode,
    case SpvOpImageSampleProjDrefExplicitLod:
    case SpvOpImageDrefGather:
       /* These all have an explicit depth value as their next source */
+      is_shadow = true;
       (*p++) = vtn_tex_src(b, w[idx++], nir_tex_src_comparator);
       break;