These are an implementation detail and should not have been
exported. This only affects Linux on platforms other than 386 and
amd64.

Fixes golang/go#30255.

Change-Id: Ib23b42a7309fd6093b6b9d8b6628de222a3928be
Reviewed-on: https://go-review.googlesource.com/c/163004
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>