Fortran: Reject missing comma in format.

	Standards require rejecting formats where descriptors
	are not separated by commas. This change allows this
	the missing comma to be accepted only with
	-std=legacy.

	PR fortran/88052

libgfortran/ChangeLog:

	* io/format.c (parse_format_list): Reject missing comma in
	format strings by default or if -std=f95 or higher. This is
	a runtime error.

gcc/testsuite/ChangeLog:

	* gfortran.dg/comma_format_extension_4.f: Add missing comma.
	* gfortran.dg/dollar_edit_descriptor_2.f: Likewise.
	* gfortran.dg/fmt_error_9.f: Likewise.
	* gfortran.dg/fmt_g0_5.f08: Likewise.
	* gfortran.dg/fmt_t_2.f90: Likewise.
	* gfortran.dg/pr88052.f90: New test.