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

[Coleen Phillimore]

On Fri, 11 Aug 2023 21:01:52 GMT, Dean Long <dlong at openjdk.org> wrote:

>> I agree but I added it to make other reviewers happy.
>
> An alternative would be to use parse_integer() instead of strtol to get the value as an int.

parse_integer is nicer so I did that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1292301035