Some preprocessors have problems if the # character isn't at position 1.

acinclude.m4

@@ -725,11 +725,11 @@ AC_DEFUN([CURL_FUNC_GETNAMEINFO_ARGTYPES], [
               ],[
 
                 int res;
-                struct sockaddr *sa=NULL;
+                struct sockaddr *sa=0;
                 $gni_arg2 salen=0;
-                char *host=NULL;
+                char *host=0;
                 $gni_arg46 hostlen=0;
-                char *serv=NULL;
+                char *serv=0;
                 $gni_arg46 servlen=0;
                 $gni_arg7 flags=0;