Add the SyscallNoError and RawSyscallNoError wrapper functions which are
used for syscalls that don't return an error. Also convert all applicable
syscalls to use these wrappers.

Updates golang/go#22924

Change-Id: Ie143abc99de8d12d36b67ac278e08d7565f73ce0
Reviewed-on: https://go-review.googlesource.com/85756
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>