re PR fortran/25106 ([4.0/4.1] statement label is zero)

re PR fortran/25106 ([4.0/4.1] statement label is zero)

	PR fortran/25106
	* parse.c (next_free): Use new prototype for gfc_match_st_label.
	Correctly emit hard error if a label is zero.
	* match.c (gfc_match_st_label): Never allow zero as a valid
	label.
	(gfc_match, gfc_match_do, gfc_match_goto): Use new prototype for
	gfc_match_st_label.
	* primary.c (): Use new prototype for gfc_match_st_label.
	* io.c (): Likewise.
	* match.h: Likewise.

From-SVN: r107999