* Makefile.in (host_hook_obj): New.
	(OBJS): Add $(host_hook_obj).
	(host_default.o): New rule.
	* config.gcc (host_hook_obj): New, default to host-default.o.
	(powerpc-*-darwin*): Use host-darwin.o.
	(out_host_hook_obj): New.
	* configure: Regenerate.
	* configure.in: Print information about out_host_hook_obj, substitute
	into output files.
	* host-default.c: New file.
	* hosthooks.h: New file.
	* toplev.c (general_init): Call host_hooks.extra_signals.
	* config/rs6000/host-darwin.c: New file.
	* config/rs6000/x-darwin: New file.
	* doc/hostconfig.texi: Add documentation for new host hook.
	Rearrange existing documentation.

From-SVN: r62470