[jdk11u-dev] RFR: 8253899: Make IsClassUnloadingEnabled signature match specification

[Vladimir Kempik]

Almost clean backport of 8253899 to jdk11u-dev. The testcase got different filename extension (c, not cpp), that had to be corrected.

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Commit messages:
 - Backport c7f00640627eab38b77d23d07876cf0247fa18f3

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/16/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=16&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/jdk11u-dev/pull/16.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/16/head:pull/16

PR: https://git.openjdk.java.net/jdk11u-dev/pull/16