Followup to wait_for_user fix

Marlin/src/Marlin.cpp

 #endif
 
 // For M109 and M190, this flag may be cleared (by M108) to exit the wait loop
-volatile bool wait_for_heatup = true;
+bool wait_for_heatup = true;
 
 // For M0/M1, this flag may be cleared (by M108) to exit the wait-for-user loop
 #if HAS_RESUME_CONTINUE

Marlin/src/Marlin.h

 inline bool IsRunning() { return  Running; }
 inline bool IsStopped() { return !Running; }
 
-extern volatile bool wait_for_heatup;
+extern bool wait_for_heatup;
 
 #if HAS_RESUME_CONTINUE
   extern bool wait_for_user;

Marlin/src/feature/emergency_parser.h

   #include "host_actions.h"
 #endif
 
-#include "../Marlin.h"
+// External references
+extern bool wait_for_user, wait_for_heatup;
+void quickstop_stepper();
 
 class EmergencyParser {