Add def `M120_M121_ENABLED` to `Configuration_adv.h`

Firmware/Configuration_adv.h

@@ -387,6 +387,12 @@ const unsigned int dropsegments=5; //everything with less than this number of st
  */
 #define EXTENDED_CAPABILITIES_REPORT
 
+/**
+ * Enable M120/M121 G-code commands
+ * 
+ */
+//#define M120_M121_ENABLED  //Be careful enabling and using these G-code commands.
+
 //===========================================================================
 //=============================  Define Defines  ============================
 //===========================================================================

Firmware/Marlin_main.cpp

@@ -6967,7 +6967,7 @@ Sigma_Exit:
       lcd_setstatus(strchr_pointer + 5);
       break;*/
 
-#if 0 //Disable these for the time being
+#ifdef M120_M121_ENABLED
     /*!
     ### M120 - Enable endstops <a href="https://reprap.org/wiki/G-code#M120:_Enable_endstop_detection">M120: Enable endstop detection</a>
     */
@@ -6981,7 +6981,7 @@ Sigma_Exit:
     case 121:
       enable_endstops(false) ;
       break;
-#endif //0
+#endif //M120_M121_ENABLED
 
     /*!
 	### M119 - Get endstop states <a href="https://reprap.org/wiki/G-code#M119:_Get_Endstop_Status">M119: Get Endstop Status</a>