RFR: JDK-8301354: Modernize utilities/breakpoint.hpp [v4]

[Justin King]

On Mon, 30 Jan 2023 17:09:23 GMT, Justin King <jcking at openjdk.org> wrote:

>> Cleanup `utilities/breakpoint.hpp` by utilizing compiler intrinsics when available, or normal signals for AIX/XLC.
>
> Justin King has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix reference to unqualified breakpoint
>   
>   Signed-off-by: Justin King <jcking at google.com>

I put this back into draft after I realized that I forgot only Clang has `__builtin_debugtrap`, making this non-ideal. Ideally GCC would have that as well.

In an ideal world, breakpoint should probably only be present in debug builds and compiled out in release builds. Additionally it should probably be consistent across platforms. But I think that ship has sailed. If GCC ever gets `__builtin_debugtrap` than this would be useful, IIF we make them used during debug builds only and fallback to `breakpoint()` calls for everything else.

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PR: https://git.openjdk.org/jdk/pull/12296