libyuv: Make Windows trybots also build with VS2013.

scripts/slave/recipes/libyuv/libyuv.expected/tryserver_libyuv_win.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\tools\\runit.py",
       "--show-path",
       "python",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\cleanup_temp.py"
     ],
@@ skipping 118 matching lines @@
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]\\gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]\\src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json",
       "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "component=shared_library dcheck_always_on=1 fastbuild=1 gomadir='[CACHE]\\cipd\\goma' target_arch=ia32 use_goma=1",
+      "GYP_MSVS_VERSION": "2013",
       "PATH": "%(PATH)s;RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]\\gn.py",
       "--root=[SLAVE_BUILD]\\src",
       "gen",
       "//out/Debug",
-      "--args=symbol_level=2 dcheck_always_on=true is_debug=true target_cpu=\"x86\" use_goma=true goma_dir=\"[CACHE]\\cipd\\goma\""
+      "--args=symbol_level=2 visual_studio_version=2013 dcheck_always_on=true is_debug=true target_cpu=\"x86\" use_goma=true goma_dir=\"[CACHE]\\cipd\\goma\""
     ],
     "cwd": "[SLAVE_BUILD]\\src",
     "name": "gn"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\tools\\runit.py",
       "--show-path",
@@ skipping 56 matching lines @@
       "libyuv_unittest.exe"
     ],
     "name": "libyuv_unittest"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]