RFR: 8357370: Export supported GCs in JVMCI

[Doug Simon]

On Tue, 20 May 2025 12:52:02 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> I need a way to detect in JVMCI if Shenandoah GC is supported (that is, built-in) by HotSpot. I need it for Shenandoah, because some vendors don't build it, but for cleanliness the relevant preprocessor constants should be exported for all GCs.
> 
> Testing:
>  - [x] build/test https://github.com/oracle/graal/pull/10904

src/hotspot/share/jvmci/vmStructs_jvmci.cpp line 498:

> 496:   declare_preprocessor_constant("ASSERT", DEBUG_ONLY(1) NOT_DEBUG(0))     \
> 497:                                                                           \
> 498:   declare_preprocessor_constant("INCLUDE_SERIALGC",     INCLUDE_SERIALGC)     \

Probably best to make the formatting consistent with how it's done for the `JVM_ACC_*` constants below (i.e., no alignment of values).

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PR Review Comment: https://git.openjdk.org/jdk/pull/25325#discussion_r2097893655