[jdk11u-dev] RFR: 8221621: FindTests.gmk cannot handle "=" in TEST.groups comments

[Joshua Cao]

clean backport

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Commit messages:
 - 8221621: FindTests.gmk cannot handle "=" in TEST.groups comments

Changes: https://git.openjdk.org/jdk11u-dev/pull/1603/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1603&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8221621
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1603.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1603/head:pull/1603

PR: https://git.openjdk.org/jdk11u-dev/pull/1603