Somehow, terribly embarrassingly, I lost part of the "re-enable
-shared on amd64" patch when rebasing before it got submitted.
This restores it and also fixes the addend to be the necessary -4.

Now updated so that Git will not put the new case into the wrong
switch.

Change-Id: I1d628232771a6d6ce6d085adf379f94a377822c5
Reviewed-on: https://go-review.googlesource.com/7126
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>