GCOV: introduce usage of terminal colors.

GCOV: introduce usage of terminal colors.

2017-10-31  Martin Liska  <mliska@suse.cz>

	* color-macros.h: New file.
	* diagnostic-color.c: Factor out color related to macros to
	color-macros.h.
	* doc/gcov.texi: Document -k option.
	* gcov.c (INCLUDE_STRING): Include string.h.
	(print_usage): Add -k option.
	(process_args): Parse it.
	(pad_count_string): New function.
	(output_line_beginning): Likewise.
	(DEFAULT_LINE_START): New macro.
	(output_lines): Support color output.

From-SVN: r254258