config.host: Add a section for generic hosts, and a subsection for Darwin.

config.host: Add a section for generic hosts, and a subsection for Darwin.

	* config.host: Add a section for generic hosts, and a subsection
	for Darwin.  Add a case for x86-darwin.  Update ppc-darwin case.
	* config/host-darwin.c: New, split out of config/rs6000/host-darwin.c.
	* config/host-darwin.h: New.
	* config/x-darwin: New.
	* config/i386/host-i386-darwin.c: New.
	* config/i386/x-darwin: New.
	* config/rs6000/host-darwin.c: Include host-darwin.h.
	(darwin_rs6000_gt_pch_get_address): Move to config/host-darwin.c.
	(darwin_rs6000_gt_pch_use_address): Likewise.
	* config/rs6000/x-darwin: Change name of .o built, update
	dependencies for changes to rs6000/host-darwin.c.

From-SVN: r97709