RFR: 8329086: Clean up java.desktop native compilation [v2]

[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.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  Make libawt CFLAGS and CXXFLAGS consistent

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18486/files
  - new: https://git.openjdk.org/jdk/pull/18486/files/ad8b1a5f..b7e31071

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18486&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18486&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 1 del; 1 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