Enable -Wextra-semi on Windows.

Requires suppressing the warning for a file generated by mc.exe,
and for a system header (which is arguably a clang bug, see comment
in the .h).

Bug: 926235
Change-Id: Iee8ecd6eab476207c1507719ba5102403f381cae
Reviewed-on: https://chromium-review.googlesource.com/c/1489102
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635689}
3 files changed