MSVC: Add support for ARM64 architecture

The v141_Link.json already appeared to have the option included, so
onlyh adding the change to v14_LIB.json.

Original header commit v3.10.0-rc1~132^2

Visual Studio 15.4 adds support for this architecture.

Templates/MSBuild/FlagTables/v14_LIB.json

@@ -34,6 +34,13 @@
     "value": "MachineARM",
     "flags": []
   },
+  {
+    "name": "TargetMachine",
+    "switch": "MACHINE:ARM64",
+    "comment": "MachineARM64",
+    "value": "MachineARM64",
+    "flags": []
+  },
   {
     "name": "TargetMachine",
     "switch": "MACHINE:EBC",