[lilliput-jdk17u:lilliput] RFR: 8319524: [Lilliput] Only warn when compact headers are explicitly enabled

[Roman Kennke]

This backports [JDK-8319524: [Lilliput] Only warn when compact headers are explicitly enabled
](https://bugs.openjdk.org/browse/JDK-8319524) to lilliput-jdk17u. The backport is not clean, because there is no ZGenerational flag to check.

 - [x] tier1 +UCOH +ZGC

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Commit messages:
 - Backport 3f73f014097262455cc42a71c32af374b77b6efd

Changes: https://git.openjdk.org/lilliput-jdk17u/pull/64/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk17u&pr=64&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319524
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/lilliput-jdk17u/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk17u.git pull/64/head:pull/64

PR: https://git.openjdk.org/lilliput-jdk17u/pull/64