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

[David Holmes]

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

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Commit messages:
 - 8348040: Bad use of ifdef with INCLUDE_xxx GC macros

Changes: https://git.openjdk.org/jdk/pull/23193/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23193&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348040
  Stats: 8 lines in 3 files changed: 0 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/23193.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23193/head:pull/23193

PR: https://git.openjdk.org/jdk/pull/23193