Use sizeof of the C type instead.

Also fix a few #undef's that got reported after my changes.

R=jarin@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I30a43b3d93e6df04fb9fb33050b52988edd7fdb1
Reviewed-on: https://chromium-review.googlesource.com/1155108Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54817}