Rs6000 native support.

Rs6000 native support.

* infptrace.c: remove #ifdef USG from around include ptrace.h.
  machines without this header should not be compiling this file.
* nm-rs6000.h, rs6000-nat.c: new files for native support.
* rs6000-tdep.c: do not include sys/ptrace.h or sys/reg.h.
* rs6000-xdep.c: removed.  all code now in rs6000-nat.c.
* xm-rs6000.h: do not include ptrace.h.
  (ATTACH_DETACH, FETCH_INFERIOR_REGISTERS): moved to nm-rs6000.h.
* config/rs6000.mh (XDEPFILES): removed rs6000-xdep.o.
  infptrace.o and inftarg.o move to NATDEPFIES.
  (NAT_FILE, NATDEPFILES): new macro for native support.