nir: add how_declared to nir_variable.data

Equivalent to the already existing how_declared at GLSL IR. The only
difference is that we are not adding all the declaration_type
available on GLSL, only the one that we will use on the short term. We
would add more mode if needed on the future.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/nir/nir.c

@@ -162,6 +162,7 @@ nir_variable_create(nir_shader *shader, nir_variable_mode mode,
    var->name = ralloc_strdup(var, name);
    var->type = type;
    var->data.mode = mode;
+   var->data.how_declared = nir_var_declared_normally;
 
    if ((mode == nir_var_shader_in &&
         shader->info.stage != MESA_SHADER_VERTEX) ||