RFR: 8264696: Multi-catch clause causes compiler exception because it uses the package-private supertype

[Guoxiong Li]

Hi all,

The method `isAccessible(Env<AttrContext> env, Type t, boolean checkInner)` should take `UnionClassType` as a special type to do some corresponding work. If not, the problem will occur. This patch fixes it and adds a test case.

Thank you for taking the time to review.

Best Regards.
-- Guoxiong

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Commit messages:
 - 8264696: Multi-catch clause causes compiler exception because it uses the package-private supertype

Changes: https://git.openjdk.java.net/jdk/pull/3374/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3374&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264696
  Stats: 118 lines in 2 files changed: 115 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3374.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3374/head:pull/3374

PR: https://git.openjdk.java.net/jdk/pull/3374