Also adds some missing asmdecl comments for funcs with Go proto.

Change-Id: Iabc68e8c0ad936e06ed719e0f030bfc5f6f6e168
Reviewed-on: https://go-review.googlesource.com/127760
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>