nir: add assertions that loops don't have a Continue Construct

Hoping that I didn't miss any, this *should* add assertions
to all functions and passes which explicitly handle 'nir_loop'.

Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13962>

src/amd/compiler/aco_instruction_selection.cpp

@@ -10340,6 +10340,7 @@ static void end_uniform_if(isel_context* ctx, if_context* ic);
 static void
 visit_loop(isel_context* ctx, nir_loop* loop)
 {
+   assert(!nir_loop_has_continue_construct(loop));
    loop_context lc;
    begin_loop(ctx, &lc);