Do not break application's signal handler installed with SA_SIGINFO

Gleb Natapov to sdl

If application installs SIGINT/SIGTERM signal handler with
sigaction(SA_SIGINFO) syscall before initializing SDL, after
initialization
of SDL signal handler will be reinstalled without SA_SIGINFO flag which
brings havoc when the signal handler is called. The breakage is done by
SDL_QuitInit()/SDL_QuitQuit() function. They use signal() to detect that
signal handler is already installed even in sigaction() is available.

src/events/SDL_quit.c

@@ -47,7 +47,19 @@ SDL_HandleSIG(int sig)
 int
 SDL_QuitInit(void)
 {
-#ifdef HAVE_SIGNAL_H
+#ifdef HAVE_SIGACTION
+    struct sigaction action;
+    sigaction(SIGINT, NULL, &action);
+    if ( action.sa_handler == SIG_DFL && action.sa_sigaction == SIG_DFL ) {
+        action.sa_handler = SDL_HandleSIG;
+        sigaction(SIGINT, &action, NULL);
+    }
+    sigaction(SIGTERM, NULL, &action);
+    if ( action.sa_handler == SIG_DFL && action.sa_sigaction == SIG_DFL ) {
+        action.sa_handler = SDL_HandleSIG;
+        sigaction(SIGTERM, &action, NULL);
+    }
+#elif HAVE_SIGNAL_H
     void (*ohandler) (int);
 
     /* Both SIGINT and SIGTERM are translated into quit interrupts */
@@ -66,7 +78,19 @@ SDL_QuitInit(void)
 void
 SDL_QuitQuit(void)
 {
-#ifdef HAVE_SIGNAL_H
+#ifdef HAVE_SIGACTION
+    struct sigaction action;
+    sigaction(SIGINT, NULL, &action);
+    if ( action.sa_handler == SDL_HandleSIG ) {
+        action.sa_handler = SIG_DFL;
+        sigaction(SIGINT, &action, NULL);
+    }
+    sigaction(SIGTERM, NULL, &action);
+    if ( action.sa_handler == SDL_HandleSIG ) {
+        action.sa_handler = SIG_DFL;
+        sigaction(SIGTERM, &action, NULL);
+    }
+#elif HAVE_SIGNAL_H
     void (*ohandler) (int);
 
     ohandler = signal(SIGINT, SIG_DFL);