ui/sdl2: use correct key names in win title on mac

ui/sdl2: use correct key names in win title on mac

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>