turn on -Wextra-semi-stmt on Windows

Just a few strays.

Change-Id: Ib209bc8dd228850b837b850dce14967a2112593e
Reviewed-on: https://skia-review.googlesource.com/c/191161
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>