[jdk11u-dev] RFR: 8249095: tools/javac/launcher/SourceLauncherTest.java fails on Windows

[Christoph Langer]

This is a clean backport of JDK-8249095, required to enable green runs of a GitHub Actions workflow.

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Depends on: https://git.openjdk.java.net/jdk11u-dev/pull/186

Commit messages:
 - 8249095: tools/javac/launcher/SourceLauncherTest.java fails on Windows

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/187/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=187&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249095
  Stats: 29 lines in 2 files changed: 21 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/187.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/187/head:pull/187

PR: https://git.openjdk.java.net/jdk11u-dev/pull/187