RFR: 8369393: NMT: poison the canaries of malloc header under ASAN build [v7]

[Afshin Zafari]

On Wed, 15 Oct 2025 07:43:40 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Kept. to be used in gtests.
>
> See comment about the `using` statements.

Done.

>> return values removed.
>
> Then we're doing a lot of special code in the implementation only for the purpose of testing. That's going to be quite surprising for the next reader. If anything, we *should* use these typedefs in the implementation.

Fixed by other changes in this PR.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27685#discussion_r2502172599
PR Review Comment: https://git.openjdk.org/jdk/pull/27685#discussion_r2502171904