RFR: JDK-8304683: Memory leak in WB_IsMethodCompatible

[Justin King]

Add missing call to `DirectivesStack::release`.

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Commit messages:
 - Fix memory leak in WB_IsMethodCompatible

Changes: https://git.openjdk.org/jdk/pull/13124/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13124&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304683
  Stats: 4 lines in 1 file changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13124.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13124/head:pull/13124

PR: https://git.openjdk.org/jdk/pull/13124