RFR: 8348040: Bad use of ifdef with INCLUDE_xxx GC macros

[Aleksey Shipilev]

On Sun, 19 Jan 2025 21:15:56 GMT, David Holmes <dholmes at openjdk.org> wrote:

> The `INCLUDE_xxx` macros should be used with `#if` not `#ifdef` as the value is alway defined as either 1 or 0. So with `#ifdef` the guard is always true. This would lead to build problems in some cases if you built a configuration without the specified GC.
> 
> Testing:
>  - tiers 1-3 sanity
>  - tiers 4-5 builds
> 
> Thanks

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/23193#pullrequestreview-2561810287