Try to get clang/win tot bots going again after VS2015 update.

tools/clang/scripts/update.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """This script is used to download prebuilt clang binaries.
 
 It is also used by package.py to build the prebuilt clang binaries."""
 
 import argparse
@@ skipping 321 matching lines @@
   # Try using the toolchain in depot_tools.
   # This sets environment variables used by SelectVisualStudioVersion below.
   sys.path.append(os.path.join(CHROMIUM_DIR, 'build'))
   import vs_toolchain
   vs_toolchain.SetEnvironmentAndGetRuntimeDllDirs()
 
   # Use gyp to find the MSVS installation, either in depot_tools as per above,
   # or a system-wide installation otherwise.
   sys.path.append(os.path.join(CHROMIUM_DIR, 'tools', 'gyp', 'pylib'))
   import gyp.MSVSVersion
-  vs_version = gyp.MSVSVersion.SelectVisualStudioVersion('2013')
+  vs_version = gyp.MSVSVersion.SelectVisualStudioVersion(
+      vs_toolchain.GetVisualStudioVersion())
   return vs_version
 
 
 def UpdateClang(args):
   print 'Updating Clang to %s...' % PACKAGE_VERSION
 
   need_gold_plugin = 'LLVM_DOWNLOAD_GOLD_PLUGIN' in os.environ or (
       sys.platform.startswith('linux') and
       'buildtype=Official' in os.environ.get('GYP_DEFINES', '') and
       'branding=Chrome' in os.environ.get('GYP_DEFINES', ''))
@@ skipping 431 matching lines @@
     args.force_local_build = True
     if 'OS=android' not in os.environ.get('GYP_DEFINES', ''):
       # Only build the Android ASan rt on ToT bots when targetting Android.
       args.with_android = False
 
   return UpdateClang(args)
 
 
 if __name__ == '__main__':
   sys.exit(main())