VS: in Clang/C2 toolset, setup correct compiler settings

Original header commit v3.6.0-rc1~279^2~10

Templates/MSBuild/FlagTables/v140_CL.json

@@ -111,6 +111,13 @@
     "value": "Disabled",
     "flags": []
   },
+  {
+    "name": "Optimization",
+    "switch": "Os",
+    "comment": "Minimize Size",
+    "value": "MinSize",
+    "flags": []
+  },
   {
     "name": "Optimization",
     "switch": "O1",

Templates/MSBuild/FlagTables/v141_CL.json

@@ -132,6 +132,13 @@
     "value": "Disabled",
     "flags": []
   },
+  {
+    "name": "Optimization",
+    "switch": "Os",
+    "comment": "Minimize Size",
+    "value": "MinSize",
+    "flags": []
+  },
   {
     "name": "Optimization",
     "switch": "O1",