VS: Add flag table entries for '/external:W*' flags in VS 16.10

Fixes: #22255

Templates/MSBuild/FlagTables/v142_CL.json

@@ -532,6 +532,41 @@
     "value": "All",
     "flags": []
   },
+  {
+    "name": "ExternalWarningLevel",
+    "switch": "external:W0",
+    "comment": "Turn Off All Warnings",
+    "value": "TurnOffAllWarnings",
+    "flags": []
+  },
+  {
+    "name": "ExternalWarningLevel",
+    "switch": "external:W1",
+    "comment": "Level1",
+    "value": "Level1",
+    "flags": []
+  },
+  {
+    "name": "ExternalWarningLevel",
+    "switch": "external:W2",
+    "comment": "Level2",
+    "value": "Level2",
+    "flags": []
+  },
+  {
+    "name": "ExternalWarningLevel",
+    "switch": "external:W3",
+    "comment": "Level3",
+    "value": "Level3",
+    "flags": []
+  },
+  {
+    "name": "ExternalWarningLevel",
+    "switch": "external:W4",
+    "comment": "Level4",
+    "value": "Level4",
+    "flags": []
+  },
   {
     "name": "CallingConvention",
     "switch": "Gd",