Avoid signal-unsafe operations in POSIX signal handler (#16160)

src/gui/guiEngine.h

@@ -14,6 +14,8 @@
 #include "util/enriched_string.h"
 #include "translation.h"
 
+#include <csignal>
+
 /******************************************************************************/
 /* Structs and macros                                                         */
 /******************************************************************************/
@@ -124,7 +126,7 @@ class GUIEngine {
 			RenderingEngine *rendering_engine,
 			IMenuManager *menumgr,
 			MainMenuData *data,
-			bool &kill);
+			volatile std::sig_atomic_t &kill);
 
 	/** default destructor */
 	virtual ~GUIEngine();
@@ -193,7 +195,7 @@ class GUIEngine {
 	irr_ptr<GUIFormSpecMenu>              m_menu;
 
 	/** reference to kill variable managed by SIGINT handler */
-	bool                                 &m_kill;
+	volatile std::sig_atomic_t           &m_kill;
 
 	/** variable used to abort menu and return back to main game handling */
 	bool                                  m_startgame = false;