Fixed compiler warning (gcc w/ -Wall) for using getpid() and kill() without

 their proper headers included.

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%402436

src/audio/arts/SDL_artsaudio.c

@@ -23,6 +23,11 @@
 
 /* Allow access to a raw mixing buffer */
 
+#ifdef HAVE_SIGNAL_H
+#include <signal.h>
+#endif
+#include <unistd.h>
+
 #include "SDL_timer.h"
 #include "SDL_audio.h"
 #include "../SDL_audiomem.h"