Support arm64 targets

[luca992]

My project requires use of arm64 targets. iOS simulator is most essential for my purposes, but mac would be great as well.

It looks like the latest easyPluginVersion:0.18.4 supports this.

[y9san9]

And also common ios target would be nice

[soywiz]

@luca992 I have moved kbignum to the korge repo that holds all the korlibs there. That repo includes arm64 targets.

@y9san9 kbignum doesn't have specific code for ios target, but has a common target and a native common target. The root build gradle configures iosCommon for all the projects. I'm not sure if that will work, since I'm not going to create a iosMain folder since that library doesn't require it. If it doesn't work, we should consider talking with the Kotlin team to figure out something to not force me to include any possible combination any other library could need.

In any case, let's wait for the next release and see if it works for you guys