ANGLE has moved onto the Windows 10 SDK, and is using new compiler
features that aren't supported by the old Windows 8.1 toolchain. Support
for the 8.1 projects has been broken in master for some time now.

Since more and more developers are moving towards Windows 10, we
are going to take a snapshot of ANGLE that includes 8.1 support and
freeze it in a branch on github.com/microsoft/angle. If developers
wish to compile for use ANGLE in 8.1 apps then they should use that
branch going forward.

Change-Id: Ifee2d8a8cc0332500e0bd338911d831e7624fa82
Reviewed-on: https://chromium-review.googlesource.com/374039
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>