VS: Populate `/permissive` flag table entry for v142

Apply the change from commit e0d6d01e52 (VS: Add flag table entry for
"permissive" flag to disable conformance mode, 2018-12-10) to the
v142 flag table.

Templates/MSBuild/FlagTables/v142_CL.json

@@ -833,10 +833,17 @@
   {
     "name": "ConformanceMode",
     "switch": "permissive-",
-    "comment": "Conformance mode",
+    "comment": "Conformance mode enabled",
     "value": "true",
     "flags": []
   },
+  {
+    "name": "ConformanceMode",
+    "switch": "permissive",
+    "comment": "Conformance mode disabled",
+    "value": "false",
+    "flags": []
+  },
   {
     "name": "TreatWChar_tAsBuiltInType",
     "switch": "Zc:wchar_t-",