Add the rawSyscallNoError wrapper function which is used for Linux
syscalls that don't return an error and convert all applicable
occurences of RawSyscall to use it instead.

Fixes #22924

Change-Id: Iff1eddb54573d459faa01471f10398b3d38528dd
Reviewed-on: https://go-review.googlesource.com/84485
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>