[lworld] RFR: 8350872: [lworld] Field is flattened although -XX:-UseFieldFlattening is set

[Frederic Parain]

Fix behavior of -UseFieldFlattening.

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Commit messages:
 - Fix UseFieldFlattening

Changes: https://git.openjdk.org/valhalla/pull/1386/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1386&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350872
  Stats: 8 lines in 2 files changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1386.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1386/head:pull/1386

PR: https://git.openjdk.org/valhalla/pull/1386