RFR: 8314114: Fix -Wconversion warnings in os code, primarily linux [v3]

[Coleen Phillimore]

On Fri, 11 Aug 2023 03:09:46 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> I started that way and it required more casts.  This was the path of least cast-ness.
>
> For some reason I have an aversion to seeing a `size_t` loop index variable. These changes to `int` are a pleasant surprise. :)

I figured if the value fits in an int and it's complaining about casting to an int, then I can just use int.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1291271068