Don't show "display"s twice in MI

Don't show "display"s twice in MI

If you run "gdb -i=mi2" and set a "display", then when "next"ing the
displays will be shown twice:

    ~"1: x = 23\n"
    ~"7\t  printf(\"%d\\n\", x);\n"
    ~"1: x = 23\n"
    *stopped,reason="end-stepping-range",frame={addr="0x0000000000400565",func="main",args=[],file="q.c",fullname="/tmp/q.c",line="7"},thread-id="1",stopped-threads="all",core="1"

The immediate cause of this is this code in mi_on_normal_stop_1:

      print_stop_event (mi_uiout);

      console_interp = interp_lookup (current_ui, INTERP_CONSOLE);
      if (should_print_stop_to_console (console_interp, tp))
	print_stop_event (mi->cli_uiout);

... which obviously prints the stop twice.

However, I think the first call to print_stop_event is intended just
to emit the MI *stopped notification, which explains why the source
line does not show up two times.

This patch fixes the bug by changing print_stop_event to only call
do_displays for non-MI-like ui-outs.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-03-19  Tom Tromey  <tromey@adacore.com>

	* mi/mi-interp.c (mi_on_normal_stop_1): Only show displays once.
	* infrun.h (print_stop_event): Add "displays" parameter.
	* infrun.c (print_stop_event): Add "displays" parameter.

gdb/testsuite/ChangeLog
2019-03-19  Tom Tromey  <tromey@adacore.com>

	* gdb.mi/mi2-cli-display.c: New file.
	* gdb.mi/mi2-cli-display.exp: New file.