Rename as M100

Marlin/Marlin_main.cpp

@@ -213,6 +213,7 @@
  * ************* SCARA End ***************
  *
  * ************ Custom codes - This can change to suit future G-code regulations
+ * M100 - Watch Free Memory (For Debugging Only)
  * M851 - Set probe's Z offset (mm above extruder -- The value will always be negative)
 
 
@@ -225,8 +226,8 @@
  *
  */
 
-#ifdef M99_FREE_MEMORY_WATCHER
-  void m99_code();
+#ifdef M100_FREE_MEMORY_WATCHER
+  void gcode_M100();
 #endif
 
 #ifdef SDSUPPORT
@@ -5378,9 +5379,9 @@ void process_next_command() {
           break;
       #endif // ENABLE_AUTO_BED_LEVELING && Z_PROBE_REPEATABILITY_TEST
 
-      #ifdef M99_FREE_MEMORY_WATCHER
-        case 99:
-          m99_code();
+      #ifdef M100_FREE_MEMORY_WATCHER
+        case 100:
+          gcode_M100();
           break;
       #endif