rt: Add a field to rust_task to hold its scheduler

src/rt/rust_builtin.cpp

@@ -417,7 +417,7 @@ start_task(rust_task_id id, fn_env_pair *f) {
 extern "C" CDECL int
 sched_threads() {
     rust_task *task = rust_task_thread::get_task();
-    return task->thread->sched->number_of_threads();
+    return task->sched->number_of_threads();
 }
 
 extern "C" CDECL rust_port*

src/rt/rust_task.cpp

@@ -233,6 +233,7 @@ rust_task::rust_task(rust_task_thread *thread, rust_task_list *state,
     ref_count(1),
     stk(NULL),
     runtime_sp(0),
+    sched(thread->sched),
     thread(thread),
     cache(NULL),
     kernel(thread->kernel),

src/rt/rust_task.h

@@ -72,10 +72,10 @@ rust_task : public kernel_owned<rust_task>, rust_cond
 
     RUST_ATOMIC_REFCOUNT();
 
-    // Fields known to the compiler.
     context ctx;
     stk_seg *stk;
     uintptr_t runtime_sp;      // Runtime sp while task running.
+    rust_scheduler *sched;
     rust_task_thread *thread;
     rust_crate_cache *cache;