nir: Add support for lowering load/stores of shared variables

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir.c

@@ -53,6 +53,7 @@ nir_shader_create(void *mem_ctx,
    shader->num_inputs = 0;
    shader->num_outputs = 0;
    shader->num_uniforms = 0;
+   shader->num_shared = 0;
 
    shader->stage = stage;