win: fix Universal Windows Platform build

This fixes a merge error in commit 7f3df804 caused by commit 332e8d61.

Additionally, this changes Curl_verify_windows_version for Windows App
builds to assume to always be running on the target Windows version.
There seems to be no way to determine the Windows version from a
UWP app. Neither GetVersion(Ex), nor VerifyVersionInfo, nor the
Version Helper functions are supported.

Bug: https://github.com/curl/curl/pull/820#issuecomment-250889878
Reported-by: Paul Joyce

Closes https://github.com/curl/curl/pull/1048