RFR: 8323170 - j2dbench is using outdated javac source/target to be able to build by itself

[Jiří Vaněk]

added workarounds so freshly built jdk can set its necessary source/taret without touching ant/makefile. In addition it can set itself as compiler/runner without putting itself on path.

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Commit messages:
 - 8323170 - j2dbench is using outdated javac source/target to be able to build by itself

Changes: https://git.openjdk.org/jdk/pull/17695/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17695&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323170
  Stats: 49 lines in 3 files changed: 43 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/17695.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17695/head:pull/17695

PR: https://git.openjdk.org/jdk/pull/17695