RFR: 7903588: asmtool can't be build by JDK 20 and above

[Leonid Kuskov]

This is a fix for [CODETOOLS-7903588](https://bugs.openjdk.org/browse/CODETOOLS-7903588)

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Commit messages:
 - 7903588: asmtool can't be build by JDK 20 and above

Changes: https://git.openjdk.org/asmtools/pull/70/files
 Webrev: https://webrevs.openjdk.org/?repo=asmtools&pr=70&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903588
  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/asmtools/pull/70.diff
  Fetch: git fetch https://git.openjdk.org/asmtools.git pull/70/head:pull/70

PR: https://git.openjdk.org/asmtools/pull/70