Add aarch64 embedded JDK config, MacOS mock toolchain settings

[ArielleA]

Hi,

This PR is for additional work to get the tests running correctly on Aarch64. One key issue was that the default embedded jvm used by default was X86_64 and does not work on other architectures.
To support this I have added a new constraint, however I will refine this in case a version of Darwin becomes available on aarch64.

I'll do the work to find a good arm32 toolchain in a future CL. I do not have access for ppc or z390 to repair those architectures.

Either way, hope this is good for you.

[hlopko]

LGTM, thanks!

[philwo]

Hi @ArielleA,

for compliance reasons we need to be able to re-mirror the source code used to build the embedded JVM. Where can we find the source-code for the linked Linaro OpenJDK build? :)

Cheers,
Philipp

[ArielleA]

Hi @philwo,

Totally understand that policy, the sourcecode is at openjdk.linaro.org. For the exact jdk in use in the Workspace the url is openjdk.linaro.org/releases/jdk9-src-1708.tar.xz.

Thanks

Arielle :)

[philwo]

Thanks, that's perfect! I'll add a comment to our release workflow and make sure that we mirror the code when we bump the OpenJDK version. :)

[buchgr]

Coming from #5661. I think it's great that we want to support aarch64, but I also think that we should have a testing strategy for it.

[philwo]

@buchgr We'd need some powerful ARM64 machines for our CI lab...

Maybe these https://www.avantek.co.uk/store/avantek-thunderx2-arm-workstation-thunderx2station.html or the Gigabyte ThunderXStation: http://thunderxforums.com/tx2home/viewtopic.php?t=3 ?

[buchgr]

@philwo 😄 ... sgtm!

[philwo]

I'm importing this change now. @dslomov told me that we had some agreement with @ArielleA on a mail thread that we'll merge this, but can't / won't officially support arm64 (e.g. with testing or official Bazel releases) until it gains more adoption.

[philwo]

@ArielleA Just FYI, I have to fix an internal test first, before I can submit it, but it's some C++ related stuff that I don't know much about... I've asked a colleague for help and we'll do this together on Monday, when he is back in the office. Sorry for the delay!