[jdk13u-dev] RFR: 8253899: Make IsClassUnloadingEnabled signature match specification

[Vladimir Kempik]

Backport for csr JDK-8268256, applies almost clean for 13u.

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Commit messages:
 - Backport c7f00640627eab38b77d23d07876cf0247fa18f3

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/236/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=236&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253899
  Stats: 20 lines in 3 files changed: 17 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/236.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/236/head:pull/236

PR: https://git.openjdk.java.net/jdk13u-dev/pull/236