VS: Update v141 CL flag table for VS 15.9

Run the command

    python3 Source/cmConvertMSBuildXMLToJSON.py -t v141 \
        'c:/.../Common7/IDE/VC/VCTargets/1033/cl.xml'

To generate `v141_CL.json` locally.  Manually move new and updated
settings over to `Templates/MSBuild/FlagTables/v141_CL.json`.

Templates/MSBuild/FlagTables/v141_CL.json

@@ -419,10 +419,31 @@
     "value": "Fast",
     "flags": []
   },
+  {
+    "name": "SpectreMitigation",
+    "switch": "Qspectre-load-cf",
+    "comment": "All Control Flow Loads",
+    "value": "SpectreLoadCF",
+    "flags": []
+  },
+  {
+    "name": "SpectreMitigation",
+    "switch": "Qspectre-load",
+    "comment": "All Loads",
+    "value": "SpectreLoad",
+    "flags": []
+  },
+  {
+    "name": "SpectreMitigation",
+    "switch": "Qspectre-",
+    "comment": "Disabled",
+    "value": "false",
+    "flags": []
+  },
   {
     "name": "SpectreMitigation",
     "switch": "Qspectre",
-    "comment": "Spectre mitigations",
+    "comment": "Enabled",
     "value": "Spectre",
     "flags": []
   },
@@ -826,7 +847,7 @@
   {
     "name": "ConformanceMode",
     "switch": "permissive-",
-    "comment": "Conformance mode enabled",
+    "comment": "Conformance mode",
     "value": "true",
     "flags": []
   },