RFR: 8314114: Fix -Wconversion warnings in os code, primarily linux [v5]

[Coleen Phillimore]

On Sat, 12 Aug 2023 12:55:30 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> I am in favour of `long` too, since that is what syscall returns. int64_t does not seem to have any obvious relation to the call. And there is no reason to need 64-bit on 32-bit Linux.
>
> We try to avoid using long in the hotspot source code, at least in the shared code since long is a different size on windows.  The preference is to use int64_t.

I suppose we can use long in platform code.  I'll change it to long.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1293384148