RFR: 8254882: ZGC: Use static_assert instead of guarantee [v2]

[Per Liden]

On Fri, 16 Oct 2020 15:35:08 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Per Liden has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add messages
>
> Marked as reviewed by tschatzl (Reviewer).

Pushed an update which adds messages to the static_asserts, since I noticed that message-less static_assert is a C++17
feature. As a side-note, I noticed that vm_version_linux_aarch64.cpp contains a few message-less static_asserts, but
gcc doesn't seem to warn about it.

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PR: https://git.openjdk.java.net/jdk/pull/696