Fix no-SMP scheduler watchdog slot selection

The scheduler watchdog only needs a slot index, and on no-SMP builds
that slot is always 0. Keep smp_scheduler_id() as an SMP-only API and
choose slot 0 locally in scheduler.c instead of providing a no-SMP
stub in smp.h.

This fixes no-SMP builds without adding a GlobalContext typedef or
watchdog-specific fallback to the SMP abstraction.

Signed-off-by: Peter M <petermm@gmail.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019cffb9-55d6-70d2-8382-88fd927bdc77
Co-authored-by: Amp <amp@ampcode.com>

Author: petermm

src/libAtomVM/scheduler.c

@@ -58,12 +58,20 @@ static int update_timer_list(GlobalContext *global)
     return (int) wait_timeout_ms;
 }
 
-static inline void scheduler_record_progress(GlobalContext *global)
+static inline int scheduler_watchdog_slot(GlobalContext *global)
 {
+#ifndef AVM_NO_SMP
     int scheduler_id = smp_scheduler_id(global);
-    if (scheduler_id < 0) {
-        scheduler_id = 0;
-    }
+    return scheduler_id < 0 ? 0 : scheduler_id;
+#else
+    UNUSED(global);
+    return 0;
+#endif
+}
+
+static inline void scheduler_record_progress(GlobalContext *global)
+{
+    int scheduler_id = scheduler_watchdog_slot(global);
     if (UNLIKELY(scheduler_id >= AVM_SCHEDULER_WATCHDOG_MAX_SLOTS)) {
         fprintf(stderr, "WARNING: scheduler_id %d exceeds AVM_SCHEDULER_WATCHDOG_MAX_SLOTS (%d), watchdog coverage lost\n",
             scheduler_id, AVM_SCHEDULER_WATCHDOG_MAX_SLOTS);

src/libAtomVM/smp.h

@@ -265,8 +265,8 @@ bool smp_is_main_thread(GlobalContext *glb);
 /**
  * @brief Return a small stable identifier for the current scheduler thread.
  *
- * @details In non-SMP builds this is always 0. In SMP builds, the main
- * scheduler is 0 and other schedulers return a positive small integer.
+ * @details The main scheduler is 0 and other schedulers return a positive
+ * small integer.
  */
 int smp_scheduler_id(GlobalContext *glb);
 
@@ -298,11 +298,6 @@ int smp_scheduler_id(GlobalContext *glb);
 #define SMP_RWLOCK_WRLOCK(lock)
 #define SMP_RWLOCK_UNLOCK(lock)
 
-static inline int smp_scheduler_id(GlobalContext *glb)
-{
-    UNUSED(glb);
-    return 0;
-}
 #endif
 
 #endif