RFR: 8253407: Move max_pow2 from test to src

[Kim Barrett]

On Mon, 21 Sep 2020 08:59:01 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> Small refactoring to move test utility function over to src, so that it can be used in both places.
> 
> Patch summary:
> - Moved the code
> - Replaced duplicate code in round_power_of_2
> - Adjusted to the surrounding powerOfTwo.hpp code and only accept integral types.
> - Added small gtest. (On the fence whether it's worth it or not)

Looks good.  The gtest seems fine, and it's already written.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/279