PR 90374 d0.d, e0.d, es0.d, en0.d, g0.d and ew.d edit descriptors.

        PR libfortran/90274
        * io/format.c (parse_format_list): Implement the E0 exponent
        width to provide smallest possible width for exponent fields.
        Refactor code for correct parsing and better readability of the
        code.
        * io/io.h (write_real_w0): Change interface to pass in pointer
        to fnode.
        * io/transfer.c: Update all calls to write_real_w0 to use the
        new interface.
        * io/write.c ((write_real_w0): Use the new interface with fnode
        to access both the decimal precision and exponent widths used in
        build_float_string.
        * io/write_float.def (build_float_string): Use the passed in
        exponent width to calculate the used width in the case of E0.

From-SVN: r279828