Currently -XX:CPUFeatures option is available only on x86_64. This complicates creating multiarch container images that are meant to be universally runnable (with -XX:CPUFeatures=generic).

I propose to make this option available on all architectures, with the non-arch specific values:
* generic
* native
* ignore

The implementation on non-x86_64 will only validate the sanity of the value.

The related option `-XX:+ShowCPUFeatures` will print an informative message (saying that the option does not make much sense).

-XX:+IgnoreCPUFeatures will be permitted as well, but it will be a no-op on the other architectures.