RFR: 8327049: Stop exporting debug.cpp functions on gcc [v2]

[Julian Waters]

On Thu, 29 Feb 2024 13:55:56 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> This is a partial backout of [JDK-8326509](https://bugs.openjdk.org/browse/JDK-8326509). It turned out that starting to export the functions from debug.cpp could have unintended consequences in certain circumstances, so revert back to the original situation where these functions were only exported on Windows.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use WINDOWS_ONLY instead

Marked as reviewed by jwaters (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/18062#pullrequestreview-1908956527