--- configure.bk	2021-02-19 15:48:10.766333301 +0900
+++ configure	2021-02-19 15:49:25.684116399 +0900
@@ -14286,6 +14286,7 @@
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#include <stdlib.h>
 
 main(){ (void)realpath("/./tmp", (void *)0); return 0; }