[lworld] RFR: 8295086: [lworld] follow-up for JDK-8288131

[Vicente Romero]

code related to primitive classes needs to be hidden behind the -XDenablePrimitiveClasses flag, this work is a follow-up of JDK-8288131. Hiding this remaining code behind the flag is not absolutely necessary as it probably won't be executed anyways but it will make easier to located, and extract if needed, the code related with primitive classes only

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Commit messages:
 - Merge branch 'lworld' into JDK-8295086
 - 8295086: [lworld] follow-up for JDK-8288131

Changes: https://git.openjdk.org/valhalla/pull/793/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=793&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295086
  Stats: 9 lines in 2 files changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/793.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/793/head:pull/793

PR: https://git.openjdk.org/valhalla/pull/793