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

[David Holmes]

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.

For the sake of moving forward, nothing further from me.

Thanks.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15229#pullrequestreview-1577855776