RFR: 8314114: Fix -Wconversion warnings in os code, primarily linux [v6]

[Coleen Phillimore]

On Thu, 10 Aug 2023 19:07:55 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Thomas Stuefe and Dean's suggestions, turn Wconversion back off.
>>  - revert copyright change
>
> src/hotspot/os/bsd/os_bsd.cpp line 2215:
> 
>> 2213:     diff = filetime1.tv_nsec - filetime2.tv_nsec;
>> 2214:   }
>> 2215:   return checked_cast<int>(diff);
> 
> Suggestion:
> 
>   return diff;

done.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1293371534