RFR: 8314114: Fix -Wconversion warnings in os code, primarily linux [v10]

[Coleen Phillimore]

On Mon, 14 Aug 2023 22:27:50 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This change fixes various -Wconversion warnings from files in the os directories and related, widening types or adding checked_cast<> where narrowing.
>> Tested with tier1 on linux/macosx/windows and tier1-4 on linux-x64-debug, windows-x64-debug.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Avoid second strlen(ebuf) with variable.

Thanks Dean, David and Thomas.  I think your comments improved the change significantly.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/15229#issuecomment-1678757944