RFR: 8349075: Once again allow -compilejdk in JAVAOPTIONS

[Magnus Ihse Bursie]

[JDK-8348905](https://bugs.openjdk.org/browse/JDK-8348905) added the possibility to set `JDK_FOR_COMPILE` on the command line to pass the `-compilejdk:` argument to jtreg. Unfortunately the way it did this meant that -compilejdk: were always passed, so trying to set it separately in JAVAOPTIONS failed due to a duplicate argument error.

This PR will instead only set  `-compilejdk:` if `JDK_FOR_COMPILE` is given on the command line.

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Commit messages:
 - 8349075: Once again allow -compilejdk in JAVAOPTIONS

Changes: https://git.openjdk.org/jdk/pull/24386/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24386&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349075
  Stats: 9 lines in 1 file changed: 5 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24386.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24386/head:pull/24386

PR: https://git.openjdk.org/jdk/pull/24386