* mi-out.c (struct ui_out_data): Replace field first_header with

* mi-out.c (struct ui_out_data): Replace field first_header with
suppress_output.
(mi_begin, mi_end): Check suppress_header.
(mi_field_int, mi_field_skip): Ditto.
(mi_field_string, mi_field_fmt): Ditto.
(mi_table_begin): When nr_rows is zero, set suppress_header else,
output the start of the header.
(mi_table_body): Clear suppress header.