RFR: build: run build and tests in parallel [v2]

[Erik Helin]

> Hi all,
> 
> please review this patch that enables builds and tests to happen in parallel. I also tweaked the build a little:
> 
> - the Gradle daemon now gets an `Xmx` of `2048 Mb`
> - Gradle will run up to 100 tests in the same JVM before forking a new one
> - the JVM for compiling will be forked, reducing heap pressure on the Gradle daemon thread
> - enabled the file system watching feature for faster rebuilds
> 
> The results on my AMD Ryzen 5 3600 is that `sh gradlew clean && sh gradlew --info test` went from ~10 minutes to ~2 minutes :partying_face: �� 
> 
> Testing:
> - [x] `make images` on Linux x64
> - [x] `make test` on Linux x64
> 
> Thanks,
> Erik

Erik Helin 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 three additional commits since the last revision:

 - Merge master
 - build: run build and tests in parallel
 - build: update to Gradle 6.8.2

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

Changes:
  - all: https://git.openjdk.java.net/skara/pull/1009/files
  - new: https://git.openjdk.java.net/skara/pull/1009/files/3c2fad55..3c2fad55

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=1009&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=1009&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/1009.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1009/head:pull/1009

PR: https://git.openjdk.java.net/skara/pull/1009