RFR: 8314114: Fix -Wconversion warnings in os code, primarily linux [v2]

[Coleen Phillimore]

On Fri, 11 Aug 2023 15:52:42 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> One of you wants checked_cast<> everywhere and another of you doesn't.  Given that we don't know from local code inspection that the result fits in an int, I chose checked_cast<> for these calls.
>
> What are the costs of checked_cast?

checked_cast instantiates a template or two. I haven't measured code bloat.  It carries risk of asserting for odd inputs that used to be truncated.  In this case, it seems like a good place to have the assert.  In obvious places, it seems like noise.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1291569289