RFR: 8351821: VMManagementImpl.c avoid switching off warnings

[Matthias Baesken]

On Fri, 14 Mar 2025 10:06:32 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> We switched off unused-variable warnings for the file VMManagementImpl.c, this should be avoided.
> This came up in [JDK-8351542](https://bugs.openjdk.org/browse/JDK-8351542) ,

In case someone has a good/better idea what to do with the ignored returned value of
`jmm_interface->GetOptionalSupport(....)`
(throwing an exception?  printing out something?)
we can do this of course too.

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PR Comment: https://git.openjdk.org/jdk/pull/24052#issuecomment-2724321246