Instead of passing four arguments to the runtime function, just pass
one pointer to a struct containing all information. This makes it much
easier to implement memory tracing in Liftoff in a follow-up CL.
Also fix a few other minor things like the namespace and the include
guards.

R=titzer@chromium.org

Change-Id: I47d8827cbb896a581585947f594af52f42bdb37c
Reviewed-on: https://chromium-review.googlesource.com/863673Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50568}