[jdk17u] RFR: 8275051: Shenandoah: Correct ordering of requested gc cause and gc request flag

[Zhengyu Gu]

I would like to backport this Shenandoah specific patch to 17u.

The patch corrects order of a couple of GC flags to ensure that GC reads the latest GC cause when a GC is requested.

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Commit messages:
 - Backport 1ab64143c06e33e23172dd77c39e434443347364

Changes: https://git.openjdk.java.net/jdk17u/pull/198/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=198&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275051
  Stats: 10 lines in 1 file changed: 5 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/198.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/198/head:pull/198

PR: https://git.openjdk.java.net/jdk17u/pull/198