perf report: Introduce --stdio-color to setup the color output mode selection

'perf report --stdio' will colorize entries with most hits and possibly
some other aspects of its output, but those colors gets suppressed if we
redirect the output to a non-tty, allow keeping the colors by adding a
new option, --stdio-color, now this use case will also output escape
sequences for colors:

$ perf annotate --stdio-color | more

Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-report.txt

···
 
 --stdio:: Use the stdio interface.
 
+--stdio-color::
+	'always', 'never' or 'auto', allowing configuring color output
+	via the command line, in addition to via "color.ui" .perfconfig.
+	Use '--stdio-color always' to generate color even when redirecting
+	to a pipe or file. Using just '--stdio-color' is equivalent to
+	using 'always'.
+
 --tui:: Use the TUI interface, that is integrated with annotate and allows
         zooming into DSOs or threads, among other features. Use of --tui
 	requires a tty, if one is not present, as when piping to other

tools/perf/builtin-report.c

···
 		    "Show raw trace event output (do not use print fmt or plugins)"),
 	OPT_BOOLEAN(0, "hierarchy", &symbol_conf.report_hierarchy,
 		    "Show entries in a hierarchy"),
+	OPT_CALLBACK_DEFAULT(0, "stdio-color", NULL, "mode",
+			     "'always' (default), 'never' or 'auto' only applicable to --stdio mode",
+			     stdio__config_color, "always"),
 	OPT_END()
 	};
 	struct perf_data_file file = {