configure: include stddef.h in udns check to get NULL

diff --git a/configure.ac b/configure.ac
index bb1e0da12db6eb7270b7c4c3eadba0a977fa06bb..486ee81e5bc107ba2525ec929f0832dcc7b28233 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -99,6 +99,7 @@ if test "$use_udns" = "yes"; then
   AC_LINK_IFELSE([AC_LANG_SOURCE([
     #include <sys/types.h>
     #include <sys/time.h>
+    #include <stddef.h>
     #include <udns.h>
     int main(void) {
       struct dns_ctx *ctx = NULL;