RFR: JDK-8306538: Zero variant build failure after JDK-8257967

[Zixian Cai]

JDK-8306538: Zero variant build failure after JDK-8257967

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Commit messages:
 - Define JvmtiAgent::set_os_lib when JVMTI feature is not available

Changes: https://git.openjdk.org/jdk/pull/13557/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13557&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306538
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13557.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13557/head:pull/13557

PR: https://git.openjdk.org/jdk/pull/13557