[master] RFR: 8319524: [Lilliput] Only warn when compact headers are explicitly enabled

[Roman Kennke]

We currently print a warning when a user specifies +UseZGC together with +UseCompactObjectHeaders. We should only print the warning when +UCOH is explicitly enabled at the command-line. This may not be very relevant at the moment, but might be in the future, or in downstreams which may want to enable compact headers by default.

When building with +UCOH by default, a number of langtools:tier1 tests are failing because of the warning.

Testing:
  - [x] langtools:tier1 (+UseZGC and hardcoded +UCOH)

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Commit messages:
 - 8319524: [Lilliput] Only warn when compact headers are explicitly enabled

Changes: https://git.openjdk.org/lilliput/pull/115/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=115&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/pull/115.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/115/head:pull/115

PR: https://git.openjdk.org/lilliput/pull/115