These comments were left behind after runtime.h was converted
from C to Go. I examined the original code and tried to move these
to the places that the most sense.

Change-Id: I8769d60234c0113d682f9de3bd8d6c34c450c188
Reviewed-on: https://go-review.googlesource.com/21969Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>