VS: Add `/arch:NotSet` flag table entries for v14x toolsets

Add `/arch:NotSet` to set `EnableEnhancedInstructionSet` to `NotSet`.

Discourse-topic: https://discourse.cmake.org/t/8892

Templates/MSBuild/FlagTables/v140_CL.json

@@ -372,7 +372,7 @@
   },
   {
     "name": "EnableEnhancedInstructionSet",
-    "switch": "",
+    "switch": "arch:NotSet",
     "comment": "Not Set",
     "value": "NotSet",
     "flags": []

Templates/MSBuild/FlagTables/v141_CL.json

@@ -393,7 +393,7 @@
   },
   {
     "name": "EnableEnhancedInstructionSet",
-    "switch": "",
+    "switch": "arch:NotSet",
     "comment": "Not Set",
     "value": "NotSet",
     "flags": []

Templates/MSBuild/FlagTables/v142_CL.json

@@ -407,7 +407,7 @@
   },
   {
     "name": "EnableEnhancedInstructionSet",
-    "switch": "",
+    "switch": "arch:NotSet",
     "comment": "Not Set",
     "value": "NotSet",
     "flags": []

Templates/MSBuild/FlagTables/v143_CL.json

@@ -407,7 +407,7 @@
   },
   {
     "name": "EnableEnhancedInstructionSet",
-    "switch": "",
+    "switch": "arch:NotSet",
     "comment": "Not Set",
     "value": "NotSet",
     "flags": []