Mips native support. Decstation and iris4 have been tested.

Mips native support.  Decstation and iris4 have been tested.
Iris3 has not.

* mips-tdep.c (supply_gregset, fill_gregset, supply_fpregset,
  fill_fpregset): removed to irix4-nat.c
* mips-xdep.c: removed.
* irix4-nat.c, mips-nat.c, nm-irix3.h, nm-irix4.h, nm-mips.h: new
  files.
* procfs.c: include nm.h.
* xm-irix3.h (U_REGS_OFFSET, FETCH_INFERIOR_REGISTERS): removed.
* xm-irix4.h: bump copyright.
(U_REGS_OFFSET, FETCH_INFERIOR_REGISTERS, USE_PROC_FS,
PROC_NAME_FMT): removed.
* xm-mips.h (FETCH_INFERIOR_REGISTERS): removed.
* config/irix4.mh (XDEPFILES): removed procfs.o fork-child.o.
(NAT_FILE, NATDEPFILES): new macros for native support.
(CC): supply default compiler switches.
* config/irix3.mh (XDEPFILES): removed infptrace.o inftarg.o fork-child.o coredep.o.
(NAT_FILE, NATDEPFILES): new macros for native support.  Note that
irix3 is untested.
* config/decstation.mh (XDEPFILES): removed infptrace.o inftarg.o
  fork-child.o mips-xdep.o coredep.o.
  (NAT_FILE, NATDEPFILES): new macros for native support.