Fix more usages of NULL without including stdio.h.

configure

@@ -10881,6 +10881,7 @@ else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+#include <stdio.h>
 #include <sys/types.h>
 #include <netdb.h>
 #include <string.h>

configure.ac

@@ -3074,6 +3074,7 @@ then
   AC_MSG_CHECKING(getaddrinfo bug)
   AC_CACHE_VAL(ac_cv_buggy_getaddrinfo,
   AC_RUN_IFELSE([AC_LANG_SOURCE([[[
+#include <stdio.h>
 #include <sys/types.h>
 #include <netdb.h>
 #include <string.h>