[lworld] RFR: 8294272: improve error messages issued by javac if primitive classes are not supported

[Vicente Romero]

improve the error message issued by javac is the `-XDenablePrimitiveClasses` is not passed by the user

-------------

Commit messages:
 - 8294272: improve error messages issued by javac if primitive classes are not supported

Changes: https://git.openjdk.org/valhalla/pull/768/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=768&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294272
  Stats: 18 lines in 7 files changed: 10 ins; 4 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/768.diff
  Fetch: git fetch https://git.openjdk.org/valhalla pull/768/head:pull/768

PR: https://git.openjdk.org/valhalla/pull/768