Merge upstream changes from Marlin 2.1.1

Marlin/src/MarlinCore.h

@@ -38,7 +38,7 @@ inline void idle_no_sleep() { idle(true); }
   extern bool G38_did_trigger;      // Flag from the ISR to indicate the endstop changed
 #endif
 
-void kill(PGM_P const lcd_error=nullptr, PGM_P const lcd_component=nullptr, const bool steppers_off=false);
+void kill(FSTR_P const lcd_error=nullptr, FSTR_P const lcd_component=nullptr, const bool steppers_off=false);
 void minkill(const bool steppers_off=false);
 
 // Global State of the firmware
@@ -61,6 +61,8 @@ bool printJobOngoing();
 bool printingIsPaused();
 void startOrResumeJob();
 
+bool printer_busy();
+
 extern bool wait_for_heatup;
 
 #if HAS_RESUME_CONTINUE