This will align the ANGLE standalone build more with Chromium.
It can catch some kinds of build break on the CQ, preventing
some churn, and also will let us cache the vs_toolchain without
needing a special named cache.

Also includes a necessary tool to cross-compile Win on Linux.

Patch series:
1. This CL
2. http://crrev.com/c/2819472
3. http://crrev.com/c/2819945

Bug: angleproject:5842
Change-Id: Idaee3b44d970d1171076a8eaa09e3e0555331d49
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2819943Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>