[OE-core] Debugging using sysroots and GDB

[Pascal Bach]

> > The only way I could get this to work is to extract both the rootfs and the rootfs-dbg into the same place and then set sysroot to that location.
> > Is this the way it is supposed to be?
>
> Yes
>
Ok I was hoping to keep them seperate.
This because I'm using the rootfs for NFS and by having the debug symbols in a seperate rootfs-dbg directory they would not be visible from the target.
By setting `PACKAGE_DEBUG_SPLIT_STYLE = "debug-file-directory"` I got this working.