[jdk17u-dev] RFR: 8269037: jsig/Testjsig.java doesn't have to be restricted to linux only

[Goetz Lindenmaier]

I backport this for parity with 17.0.3-oracle.

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Commit messages:
 - Backport 34ba70a71ba414a6d8cfc5c667d556d4d6072793

Changes: https://git.openjdk.java.net/jdk17u-dev/pull/70/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u-dev&pr=70&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269037
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk17u-dev/pull/70.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u-dev pull/70/head:pull/70

PR: https://git.openjdk.java.net/jdk17u-dev/pull/70