* toplev.c (display_help): Fix thinko in documentation.

	* diagnostic.h (output_buffer::indent_skip): New fields.
	(output_indentation): New macro.

	* diagnostic.c (output_indent): New function.
	(output_set_prefix, clear_diagnostic_info): Use.
	(output_emit_prefix): Predict future indentation.

From-SVN: r36205