x86 automatically truncates the shift amount to be 5-bits. But not
all architectures do that.

R=rossberg@chromium.org, jarin@chromium.org, joransiu@ca.ibm.com, bjaideep@ca.ibm.com
BUG=

Review-Url: https://codereview.chromium.org/2616743002
Cr-Commit-Position: refs/heads/master@{#42099}