Should pass -msave-args when building

[richlowe]

The GCC normally used on illumos systems is patched to support -msave-args, a GCC analogue of Studio's -Wu,-save_args, which pushes all register-passed arguments to the stack such that mdb can then find them on amd64.

It'd be a lot easier to debug in the kvm module if it was built with this flag, too.