[yocto] Building SDK for macOS

[Andy Pont]

Ross wrote...

>Did a little poking.
>
>The need to build a SDK tarball on an existing macOS could probably be removed by using one of the convenient tarballs from https://github.com/phracker/MacOSX-SDKs/releases.
>
>The SDK is 32-bit, which is going to be an issue on modern macOS systems.
>
>The layer has several versioned bbappends which need updating to work with recent releases.
>
>None of this is insurmountable, meta-darwin has been used for products in the past and with a little effort can be made to do so again.
Thanks for the feedback. If time allows I may take a look into some of 
these issues and see if they are resolvable. In the meantime, I think a 
headless Linux VM with SSH and NFS support enabled might be the quicker 
route to follow.

-Andy.