diff -ruN postgresql-9.6.20-orig/configure postgresql-9.6.20/configure
--- postgresql-9.6.20-orig/configure	2020-11-09 16:32:22.000000000 -0600
+++ postgresql-9.6.20/configure	2021-01-23 06:01:25.000000000 -0600
@@ -11723,6 +11723,7 @@
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#include <stdlib.h>
 #include <time.h>
 #ifndef tzname /* For SGI.  */
 extern char *tzname[]; /* RS6000 and others reject char **tzname.  */
@@ -13809,6 +13810,7 @@
 # trust that the arithmetic works.
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#include <stdlib.h>
 
 int
 main ()
@@ -13830,6 +13832,7 @@
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#include <stdlib.h>
 typedef long int ac_int64;
 
 /*
@@ -13893,6 +13896,7 @@
 # trust that the arithmetic works.
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#include <stdlib.h>
 
 int
 main ()