VS: Do not apply any '/external:*' flag table mapping on VS < 16.10

Since commit 887e9df0 (VS: Update v142 CL flag table for VS 16.10,
2021-06-04) we map several `/external:*` flags to their corresponding
`.vcxproj` elements.  These elements were added to `cl.xml` in VS 16.10,
so filter them out in older VS versions.  Add a field to the json flag
table format to specify the minimum version of VS needed for a given
mapping.

Issue: #22308

Source/cmGlobalVisualStudio10Generator.cxx

@@ -1361,8 +1361,6 @@ static unsigned int cmLoadFlagTableSpecial(Json::Value entry,
 
 namespace {
 
-std::string const vsVer16_10_0 = "16.10.31321.278";
-
 cmIDEFlagTable const* cmLoadFlagTableJson(std::string const& flagJsonPath,
                                           cm::optional<std::string> vsVer)
 {
@@ -1380,18 +1378,22 @@ cmIDEFlagTable const* cmLoadFlagTableJson(std::string const& flagJsonPath,
       if (reader.parse(stream, flags, false) && flags.isArray()) {
         std::vector<cmIDEFlagTable> flagTable;
         for (auto const& flag : flags) {
+          Json::Value const& vsminJson = flag["vsmin"];
+          if (vsminJson.isString()) {
+            std::string const& vsmin = vsminJson.asString();
+            if (!vsmin.empty()) {
+              if (!vsVer ||
+                  cmSystemTools::VersionCompareGreater(vsmin, *vsVer)) {
+                continue;
+              }
+            }
+          }
           cmIDEFlagTable flagEntry;
           flagEntry.IDEName = cmLoadFlagTableString(flag, "name");
           flagEntry.commandFlag = cmLoadFlagTableString(flag, "switch");
           flagEntry.comment = cmLoadFlagTableString(flag, "comment");
           flagEntry.value = cmLoadFlagTableString(flag, "value");
           flagEntry.special = cmLoadFlagTableSpecial(flag, "flags");
-          // FIXME: Port this version check to a Json field.
-          if (vsVer &&
-              !cmSystemTools::VersionCompareGreaterEq(*vsVer, vsVer16_10_0) &&
-              flagEntry.IDEName == "ExternalWarningLevel") {
-            continue;
-          }
           flagTable.push_back(flagEntry);
         }
         cmIDEFlagTable endFlag{ "", "", "", "", 0 };

Templates/MSBuild/FlagTables/v142_CL.json

@@ -572,6 +572,7 @@
     "switch": "external:W0",
     "comment": "Turn Off All Warnings",
     "value": "TurnOffAllWarnings",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -579,6 +580,7 @@
     "switch": "external:W1",
     "comment": "Level1",
     "value": "Level1",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -586,6 +588,7 @@
     "switch": "external:W2",
     "comment": "Level2",
     "value": "Level2",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -593,6 +596,7 @@
     "switch": "external:W3",
     "comment": "Level3",
     "value": "Level3",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -600,6 +604,7 @@
     "switch": "external:W4",
     "comment": "Level4",
     "value": "Level4",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -1141,6 +1146,7 @@
     "switch": "external:anglebrackets",
     "comment": "Treat Files Included with Angle Brackets as External",
     "value": "true",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -1148,6 +1154,7 @@
     "switch": "external:templates-",
     "comment": "Template Diagnostics in External Headers",
     "value": "true",
+    "vsmin": "16.10.31321.278",
     "flags": []
   },
   {
@@ -1277,6 +1284,7 @@
     "switch": "external:env:",
     "comment": "External Directories Environment Variables",
     "value": "",
+    "vsmin": "16.10.31321.278",
     "flags": [
       "UserValue",
       "SemicolonAppendable"