src/filesystem/unix/SDL_sysfilesystem.c add <stdio.h> inclusion

gets rid of some warnings

src/filesystem/unix/SDL_sysfilesystem.c

@@ -25,6 +25,7 @@
 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 /* System dependent filesystem routines                                */
 
+#include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <dirent.h>