re PR libfortran/90374 (Fortran 2018: Support d0.d, e0.d, es0.d, en0.d, g0.d and ew.d e0 edit descriptors for output)

2019-11-06  Jerry DeLisle  <jvdelisle@gcc.ngu.org>

	PR fortran/90374
	* io.c (check_format): Allow zero width for D, E, EN, and ES
	specifiers as default and when -std=F2018 is given. Retain
	existing errors when using the -fdec family of flags.

	* libgfortran/io/format.c (parse_format_list): Relax format checking for
	zero width as default and when -std=f2018.
	io/format.h (format_token): Move definition to io.h.
	io/io.h (format_token): Add definition here to allow access to
	this definition at higher levels. Rename the declaration of
	write_real_g0 to write_real_w0 and add a new format_token
	argument, allowing higher level functions to pass in the
	token for handling of g0 vs the other zero width specifiers.
	io/transfer.c (formatted_transfer_scalar_write): Add checks for
	zero width and call write_real_w0 to handle it.
	io/write.c (write_real_g0): Remove.
	(write_real_w0): Add new, same as previous write_real_g0 except
	check format token to handle the g0 case.

	* gfortran.dg/fmt_error_10.f: Modify for new constraints.
	* gfortran.dg/fmt_error_7.f: Add dg-options "-std=f95".
	* gfortran.dg/fmt_error_9.f: Modify for new constraints.
	* gfortran.dg/fmt_zero_width.f90: New test.

From-SVN: r277905