VS: Populate `/JMC-` flag table entry for v142

Add the negative form of the option.

Templates/MSBuild/FlagTables/v142_CL.json

@@ -595,6 +595,13 @@
     "value": "Send",
     "flags": []
   },
+  {
+    "name": "SupportJustMyCode",
+    "switch": "JMC-",
+    "comment": "Support Just My Code Debugging",
+    "value": "false",
+    "flags": []
+  },
   {
     "name": "SupportJustMyCode",
     "switch": "JMC",