RFR: 8361216: Do not fork javac in J2DBench ant build

[Eric Caspole]

Build J2DBench in ant using JAVA_HOME, not using fork to possibly pick a different javac from the PATH.

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Commit messages:
 - 8361216: Do not fork javac in J2DBench ant build

Changes: https://git.openjdk.org/jdk/pull/26077/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26077&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361216
  Stats: 8 lines in 1 file changed: 0 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/26077.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26077/head:pull/26077

PR: https://git.openjdk.org/jdk/pull/26077