Fix #1038: Consider unsupported platforms as exotic

[parttimenerd]

Only fall back on Linuxx64 on platforms not mentioned in
https://github.com/torvalds/linux/blob/5bfc75d92efd494db37f5c4c173d3639d4772966/tools/perf/scripts/python/Perf-Trace-Util/lib/Perf/Trace/Util.py#L56
(excluding the i*86 platforms).
This prevents the installation of a x86_64 JDK on PowerPC (and multiple other platforms).

Fixes #1038.

[marc0der]

@parttimenerd happy to improve this, but I do expect some test coverage here. The appropriate test to look at is the PlatformSpec.

Also, I would be as bold as to say that we should make Exotic the fallthrough option, and ensure that x86_64 really is the only possibility for standard 64 bit Linux architecture.

Finally, we also need to ensure that the backend knows what to do with Exotic.

[parttimenerd]

Thanks for the review. I will look into adding test coverage next week.

[marc0der]

@parttimenerd I'd still be really keen to take this forward if you were willing to take this on. Please shout if you need any help with tests.

[parttimenerd]

I had other JDK work to do, but I'm going to look into it this evening.

[parttimenerd]

I've modified the PR accordingly and added a PR (sdkman/sdkman-broker#15) to sdkman-broker. Is there anything more to do?

[marc0der]

@parttimenerd Thanks for contributing this! I had to rebase against master and GitHub was not smart enough to pick that up. I also fixed some of the failing tests. Your changes are now merged and available for testing on the beta channel. Please let me know if this fixes your issues.