RFR: JDK-8267839: trivial mem leak in numa

[Hamlin Li]

There is a trivial mem leak in numa related code. This patch is to use a stored bitmask* rather than get a new one.

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Commit messages:
 - numa.leak

Changes: https://git.openjdk.java.net/jdk/pull/4219/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4219&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267839
  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4219.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4219/head:pull/4219

PR: https://git.openjdk.java.net/jdk/pull/4219