[jdk21] RFR: 8305671: javac rejects semicolons in compilation units with no imports

[Archie Cobbs]

This pull request contains a backport of commit [a08352f6](https://github.com/openjdk/jdk/commit/a08352f62181d7ae010851959b35d1e11a184f40) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.

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Commit messages:
 - Backport a08352f62181d7ae010851959b35d1e11a184f40

Changes: https://git.openjdk.org/jdk21/pull/64/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=64&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305671
  Stats: 92 lines in 2 files changed: 89 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk21/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/64/head:pull/64

PR: https://git.openjdk.org/jdk21/pull/64