Include missing header files which define functions for which gcc has

builtints (e.g., exit, strcmp).

usr.bin/talk/get_names.c

@@ -41,6 +41,7 @@ static const char rcsid[] =
 
 #include <err.h>
 #include <pwd.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/param.h>
 #include "talk.h"

usr.bin/talk/init_disp.c

@@ -46,6 +46,7 @@ static const char rcsid[] =
 
 #include <err.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <termios.h>