build: Assert that Win cross-builds from Mac are 64-bit.

Bug: 794838
Change-Id: I9bdf48936e28a1ae788fa1277ac664e1eab1d9e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1844787
Commit-Queue: Hans Wennborg <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/master@{#703292}
2 files changed