RFR: 8259894: refactor parts of jvm.h into jvm_io.h and jvm_constants.h [v2]

[Ioi Lam]

On Fri, 22 Jan 2021 23:24:52 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   David Holmes comments
>
> Looks good to me.

Thanks @coleenp and @dholmes-ora for the review!

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PR: https://git.openjdk.java.net/jdk/pull/2154