* configure.in: Add Lynx/rs6000 support.

	* configure.in:  Add Lynx/rs6000 support.
	* lynx-nat.c:  Clean up some Sparc stuff.  Clean up ptrace error
	messages.  Add rs6000 support.  Don't try to modify unwritable
	registers.
	* rs6000-nat.c:  Move lots of native dependent stuff (like core
	file support) from rs6000-tdep.c & xcoffexec.c to here.
	* rs6000-tdep.c:  Move native dependent stuff to nat.c.
	* xcoffexec.c:  Move native dependent stuff to nat.c.
	* config/rs6000/nm-rs6000.h:  Move defs of SOLIB_* macros to here
	from tm	file.
	* config/rs6000/tm-rs6000.h:  Remove defs of SOLIB_* funcs, cuz they're
	really native.
	* config/rs6000/tm-rs6000lynx.h, config/rs6000/xm-rs6000lynx.h:
	New files to support Lynx/rs6000.