RFR: 8268478: JVMCI tests failing after JDK-8268052

[Tom Rodriguez]

I was missing a lock acquire in the new make_in_use call.  mach5 testing is underway.

-------------

Commit messages:
 - 8268478: JVMCI tests failing after JDK-8268052

Changes: https://git.openjdk.java.net/jdk/pull/4442/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4442&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268478
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4442.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4442/head:pull/4442

PR: https://git.openjdk.java.net/jdk/pull/4442