RFR: Build: Update to JDK 15.0.2 [v2]

[Andrea Cosentino]

> Hello all,
> 
> Just a little PR for upgrading to JDK 15.0.2.
> 
> make images passed fine and make test too.
> 
> Thank you

Andrea Cosentino has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains one additional commit since the last revision:

  Build: Update to JDK 15.0.2

-------------

Changes:
  - all: https://git.openjdk.java.net/skara/pull/989/files
  - new: https://git.openjdk.java.net/skara/pull/989/files/02430fb1..2a28e266

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=989&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=989&range=00-01

  Stats: 585 lines in 23 files changed: 454 ins; 49 del; 82 mod
  Patch: https://git.openjdk.java.net/skara/pull/989.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/989/head:pull/989

PR: https://git.openjdk.java.net/skara/pull/989