Fix "no effect" and "unused variable" compile warnings (#12473)

Marlin/src/core/macros.h

@@ -196,7 +196,7 @@
 #define MMM_TO_MMS(MM_M) ((MM_M)/60.0f)
 #define MMS_TO_MMM(MM_S) ((MM_S)*60.0f)
 
-#define NOOP (0)
+#define NOOP (void(0))
 
 #define CEILING(x,y) (((x) + (y) - 1) / (y))
 

Marlin/src/feature/power_loss_recovery.cpp

@@ -216,6 +216,8 @@ void PrintJobRecovery::write() {
   const int16_t ret = file.write(&info, sizeof(info));
   #if ENABLED(DEBUG_POWER_LOSS_RECOVERY)
     if (ret == -1) SERIAL_ECHOLNPGM("Power-loss file write failed.");
+  #else
+    UNUSED(ret);
   #endif
 }