Add missing #include.

Commit 31400a673 and siblings added a check_stack_depth() call in
contrib/intarray/_int_bool.c, but neglected to note that in our oldest
branches that file didn't have the #include that defines that function.
This results in a fortunately-harmless compiler warning.  Per buildfarm.

contrib/intarray/_int_bool.c

@@ -3,6 +3,7 @@
  */
 #include "postgres.h"
 
+#include "miscadmin.h"
 #include "utils/builtins.h"
 
 #include "_int.h"