The Apple gdbstub protocol is different from the normal gdbstub protocol
used on PowerPC. Add support for the different variant, so that we can use
Apple's gdb to debug guest code.
Keep in mind that the switch is a compile time option. We can't detect
during runtime whether a gdb connecting to us is an upstream gdb or an
Apple gdb.
Signed-off-by: Alexander Graf <agraf@suse.de>