RFR: use a staic final for "old-m-a-i-n" thread name

[Chris Plummer]

use a staic final for "old-m-a-i-n" thread name

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Commit messages:
 - use a staic final for 'old-m-a-i-n'

Changes: https://git.openjdk.java.net/loom/pull/151/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=151&range=00
  Stats: 19 lines in 5 files changed: 3 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/loom/pull/151.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/151/head:pull/151

PR: https://git.openjdk.java.net/loom/pull/151