Previously, when using the SDL2 UI on MacOS, the title bar uses incorrect
key names (such as Ctrl and Alt instead of the standard MacOS key symbols
like ⌃ and ⌥). This commit changes sdl_update_caption in ui/sdl2.c to
use the correct symbols when compiling for MacOS (CONFIG_DARWIN is
defined).

Unfortunately, standard Mac keyboards do not include a "Right-Ctrl" key,
so in the case that the SDL grab mode is set to HOT_KEY_MOD_RCTRL, the
default text is still used.

Signed-off-by: Adrian Wowk <dev@adrianwowk.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231030024119.28342-1-dev@adrianwowk.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>