* mkconfig.sh: Output to config.h, hconfig.h and tconfig.h
 	forward defs for struct tags rtx_def, union_tree, rtvec_def
 	also output corresponding typedefs for rtxm, tree, and rtvcec.

 	* system.h: Move forward defs for struct tags rtx_def, union_tree,
 	rtvec_def along with corresponding typedefs for rtx, tree, and
 	rtvcec to config.h, hconfig.h, tconfig.h

From-SVN: r48499