Implement Alt+F4 on non-Windows desktops

[fdelapena]

To proper emulate this key combination behavior used by RPG_RT even in fullscreen mode.

[fdelapena]

Removing _WIN32 ifdef works fine on GNU/Linux desktop.
Are these keysims getting issues on specific ports to have this ifdef'd?

diff --git a/src/sdl_ui.cpp b/src/sdl_ui.cpp
index 86c9244..1f04da2 100644
--- a/src/sdl_ui.cpp
+++ b/src/sdl_ui.cpp
@@ -624,13 +624,13 @@ void SdlUi::ProcessKeyDownEvent(SDL_Event &evnt) {
 #if defined(USE_KEYBOARD) && defined(SUPPORT_KEYBOARD)
        switch (evnt.key.keysym.sym) {
        case SDLK_F4:
-#ifdef _WIN32
                // Close program on LeftAlt+F4
                if (evnt.key.keysym.mod & KMOD_LALT) {
                        Player::exit_flag = true;
                        return;
                }
-#endif

                // Toggle fullscreen on F4 and no alt is pressed
                if (!(evnt.key.keysym.mod & KMOD_RALT) && !(evnt.key.keysym.mod & KMOD_LALT)) {

[Ghabry]

Possible that it was fixed by some window manager update in the last two years which resolved this issue for us ;)