There is just one version now, called IsPowerOfTwo. It accepts any
integral type.
There is one slight semantical change: Called with kMinInt, it
previously returned true, because the argument was implicitly casted to
an unsigned. It's now (correctly) returning false, so I had to add
special handlings of kMinInt in machine-operator-reducer before calling
IsPowerOfTwo on that value.

R=mlippautz@chromium.org,mstarzinger@chromium.org,jgruber@chromium.org,ishell@chromium.org,yangguo@chromium.org

Change-Id: Idc112a89034cdc8c03365b778b33b1c29fefb38d
Reviewed-on: https://chromium-review.googlesource.com/568140Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46627}