[lworld] RFR: 8287767: [lw4] Javac tolerates mutually incompatible super types.

[Srikanth Adayapalam]

Restore behavior inadvertently deleted earlier.

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Commit messages:
 - 8287767: [lw4] Javac tolerates mutually incompatible super types.

Changes: https://git.openjdk.java.net/valhalla/pull/705/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=705&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287767
  Stats: 48 lines in 5 files changed: 39 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/705.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/705/head:pull/705

PR: https://git.openjdk.java.net/valhalla/pull/705