The old write barriers used _nostore versions, which
don't work for Ian's cgo checker. Instead, we adopt the
same write barrier pattern as the default compiler.
It's a bit trickier to code up but should be more efficient.
Change-Id: I6696c3656cf179e28f800b0e096b7259bd5f3bb7
Reviewed-on: https://go-review.googlesource.com/18941
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>