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

[Thomas Stuefe]

On Fri, 11 Aug 2023 20:58:19 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Put back size_t parameter for print_signal_handlers and add a checked_cast<> future could fix the dll_address_to_x functions.
>
> src/hotspot/os/linux/os_linux.cpp line 404:
> 
>> 402: // thread id is used to access /proc.
>> 403: pid_t os::Linux::gettid() {
>> 404:   int64_t rslt = syscall(SYS_gettid);
> 
> Suggestion:
> 
>   long rslt = syscall(SYS_gettid);

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.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15229#discussion_r1292102288