nir: Initialize workgroup_size in builder_init_simple_shader

It can't be 0 in Vulkan.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24158>

src/compiler/nir/nir_builder.c

@@ -50,6 +50,13 @@ nir_builder_init_simple_shader(gl_shader_stage stage,
    /* Simple shaders are typically internal, e.g. blit shaders */
    b.shader->info.internal = true;
 
+   /* Compute shaders on Vulkan require some workgroup size initialized, pick
+    * a safe default value. This relies on merging workgroups for efficiency.
+    */
+   b.shader->info.workgroup_size[0] = 1;
+   b.shader->info.workgroup_size[1] = 1;
+   b.shader->info.workgroup_size[2] = 1;
+
    return b;
 }