In change crrev.com/1504983002 the include\ucrt path from
the Windows 10 SDK was added to the include search path,
but this is not a legal thing to do on VS 2013. This change
makes the ucrt path VS 2015 specific.

Testing shows that this makes no difference to the VS 2015
package.

BUG=440500

Review URL: https://codereview.chromium.org/1609933004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@298330 0039d316-1c4b-4281-b951-d872f2087c98