RFR: 8334391: JDK build should exclude *-files directories for Java source

[Magnus Ihse Bursie]

We should always exclude `doc-files` and `snippet-files` when compiling java code. To generalize this, exclude all `*-files` directories.

(The usage of EXCLUDES and EXCLUDE_FILES is a bit weird. In essence, EXCLUDE_FILES prepends a `%` wildchar match to the filenames given, which we use here, while EXCLUDES matches only strict directory names in the path. These should probably be clarified/redesigned for more intuitive exclusion.)

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Commit messages:
 - 8334391: JDK build should exclude *-files directories for Java source

Changes: https://git.openjdk.org/jdk/pull/24449/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24449&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334391
  Stats: 36 lines in 7 files changed: 18 ins; 17 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24449.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24449/head:pull/24449

PR: https://git.openjdk.org/jdk/pull/24449