Extends CL 132435 to s390x. s390x has 32- and 64-bit variable
rotate left instructions.

Change-Id: Ic4f1ebb0e0543207ed2fc8c119e0163b428138a5
Reviewed-on: https://go-review.googlesource.com/133035
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>