Auto-download Win SDK on non-Win hosts if 'win' is in target_os in .gclient.

Also, automatically set up a case-insensitive user-space file system mount
for the Windows SDK when on Linux.

This implements https://bugs.chromium.org/p/chromium/issues/detail?id=495204#c82

Bug: 495204
Change-Id: I8c6833570bfffffcfd9b52f31a5ee5e620f46620
Reviewed-on: https://chromium-review.googlesource.com/713999
Reviewed-by: Hans Wennborg <[email protected]>
Commit-Queue: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/master@{#508375}
2 files changed