--- configure.orig	2020-06-29 23:03:57.000000000 +1000
+++ configure	2020-06-29 23:06:58.000000000 +1000
@@ -3377,7 +3377,7 @@
   # has no effect, don't bother defining them
   Darwin/[6789].*)
     define_xopen_source=no;;
-  Darwin/1[0-9].*)
+  Darwin/[12][0-9].*)
     define_xopen_source=no;;
   # On AIX 4 and 5.1, mbstate_t is defined only when _XOPEN_SOURCE == 500 but
   # used in wcsnrtombs() and mbsnrtowcs() even if _XOPEN_SOURCE is not defined