--- configure
+++ configure
@@ -21478,8 +21478,9 @@
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#include <stdlib.h>
 #include <semaphore.h>
-main () {
+int main () {
   struct s {
     char a;
     union { long long x; sem_t y; } b;
@@ -21514,7 +21515,8 @@
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-main () {
+#include <stdlib.h>
+int main () {
   struct s {
     char a;
     double b;