VS: Populate -Qspectre- flag table entry for v143

Apply the change from commit 43aa632f57 (VS: Populate `-Qspectre-` flag
table entry for v142, 2019-01-24, v3.14.0-rc1~74^2~7) to the v143 flag
table.  Sort the longer options before the shorter ones.  Remove the
default variant with an empty switch.

Templates/MSBuild/FlagTables/v143_CL.json

@@ -428,9 +428,9 @@
   },
   {
     "name": "SpectreMitigation",
-    "switch": "Qspectre",
+    "switch": "Qspectre-load-cf",
-    "comment": "Enabled",
+    "comment": "All Control Flow Loads",
-    "value": "Spectre",
+    "value": "SpectreLoadCF",
     "flags": []
   },
   {
@@ -442,16 +442,16 @@
   },
   {
     "name": "SpectreMitigation",
-    "switch": "Qspectre-load-cf",
+    "switch": "Qspectre-",
-    "comment": "All Control Flow Loads",
+    "comment": "Disabled",
-    "value": "SpectreLoadCF",
+    "value": "false",
     "flags": []
   },
   {
     "name": "SpectreMitigation",
-    "switch": "",
+    "switch": "Qspectre",
-    "comment": "Disabled",
+    "comment": "Enabled",
-    "value": "false",
+    "value": "Spectre",
     "flags": []
   },
   {