RFR: 7903191: Fix build with "MAKEFLAGS=-j32".

[Jan Kratochvil]

A parallel build needlessly errors out:

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Commit messages:
 - Fix build with "MAKEFLAGS=-j32".

Changes: https://git.openjdk.java.net/jtreg/pull/72/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=72&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903191
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/72.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/72/head:pull/72

PR: https://git.openjdk.java.net/jtreg/pull/72