RFR: 8337241: Shenandoah: Normalize include guards [v2]

[William Kemper]

> Some of the include guards are not like the others.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Add missing whitespace

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20342/files
  - new: https://git.openjdk.org/jdk/pull/20342/files/cbf28d70..eabbddfc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20342&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20342&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20342.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20342/head:pull/20342

PR: https://git.openjdk.org/jdk/pull/20342