RFR: CODETOOLS-7902842: jcstress: fix numeric promotions

[Aleksey Shipilev]

SonarCloud instance reports multiple places where numeric promotions are problematic. We need to fix these.

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Commit messages:
 - CODETOOLS-7902842: jcstress: fix numeric promotions

Changes: https://git.openjdk.java.net/jcstress/pull/8/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=8&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902842
  Stats: 13 lines in 4 files changed: 6 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/8.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/8/head:pull/8

PR: https://git.openjdk.java.net/jcstress/pull/8