RFR: 8253285: Some java/util/StringJoiner tests do not explicitly specify required -XX:+CompactStrings

[Andrew Leonard]

Signed-off-by: Andrew Leonard <andrew_m_leonard at uk.ibm.com>

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Commit messages:
 - 8253285: Some java/util/StringJoiner tests do not explicitly specify required -XX:+CompactStrings

Changes: https://git.openjdk.java.net/jdk/pull/223/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=223&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253285
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/223.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/223/head:pull/223

PR: https://git.openjdk.java.net/jdk/pull/223