GN: Fix single-file compilations in VS2017 projects

Setting the "WindowsTargetPlatformVersion" XML element seems to
be necessary in VS2017. Single-file compilations do not work
without it. It does not cause any problems in older VS versions.

R=brettw@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2858273002
Cr-Original-Commit-Position: refs/heads/master@{#472272}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d77555bcaf03f30f100c8ac72d598d14ef63153f
1 file changed
tree: 44b338d99543c5d11eaa6a19cb8db6c8eeb33a97
  1. tools/