cselib_record_sets_hook takes an rtx_insn

gcc/
	* cselib.h (cselib_record_sets_hook):  Strengthen initial param
	"insn" from rtx to rtx_insn *.

	* cselib.c (cselib_record_sets_hook): Likewise.

	* var-tracking.c (add_with_sets): Likewise, renaming back from
	"uncast_insn" to "insn" and eliminating the checked cast from rtx
	to rtx_insn *.

From-SVN: r214535