RFR: 8329086: Clean up java.desktop native compilation

[Magnus Ihse Bursie]

This is a follow-up on [JDK-8328680](https://bugs.openjdk.org/browse/JDK-8328680), making the same kind of cleanup to java.desktop. Some code needed more special treatment here, so there is some additional effects outside of the modules/java.desktop directory. The code was also in worse shape than other modules, so some additional changes to the build logic where needed.

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Commit messages:
 - Unify windows and unix build of jawt
 - Move bundled/system libfreetype logic to libfontmanager
 - * Setup LIBJPEG_LIBS and GIFLIB_LIBS in configure.
 - Trivial cleanups in java.desktop

Changes: https://git.openjdk.org/jdk/pull/18486/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18486&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329086
  Stats: 605 lines in 4 files changed: 205 ins; 218 del; 182 mod
  Patch: https://git.openjdk.org/jdk/pull/18486.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18486/head:pull/18486

PR: https://git.openjdk.org/jdk/pull/18486