RFR: 8285506: Unify os::vsnprintf implementations

[David Holmes]

We now only need a single shared definition of os::vsnprintf.

Testing - tiers 1-3 (sanity)

Thanks.

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Commit messages:
 - 8285506: Unify os::vsnprintf implementations

Changes: https://git.openjdk.org/jdk/pull/19422/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19422&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8285506
  Stats: 34 lines in 4 files changed: 10 ins; 22 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19422.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19422/head:pull/19422

PR: https://git.openjdk.org/jdk/pull/19422