RFR: build: update to JDK 15.0.1 [v2]

[Erik Helin]

> Hi all,
> 
> please review this patch that updates the JDK used for building Skara to 15.0.1.
> 
> Testing:
> - [x] `make images`
> - [x] `make test`
> 
> Thanks,
> Erik

Erik Helin has updated the pull request incrementally with one additional commit since the last revision:

  Use explicit newline pattern

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

Changes:
  - all: https://git.openjdk.java.net/skara/pull/969/files
  - new: https://git.openjdk.java.net/skara/pull/969/files/f5f30956..26c700c3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=969&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=969&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/969.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/969/head:pull/969

PR: https://git.openjdk.java.net/skara/pull/969