We are no longer able to use the kernel bug for detecting the execution
of 386 emulation on 11.2-RELEASE or above kernels. This change uses a
variable that holds the execution mode detected in init instead.

Change-Id: Ib6afdbc40ae1feb8caf040c64c4b01971efc6325
Reviewed-on: https://go-review.googlesource.com/c/139917
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>