Patch #1540470, for OpenBSD 4.0. Backport candidate for 2.[34].
diff --git a/configure b/configure
index 5bbccce..b96349a 100755
--- a/configure
+++ b/configure
@@ -1553,7 +1553,7 @@
# On OpenBSD, select(2) is not available if _XOPEN_SOURCE is defined,
# even though select is a POSIX function. Reported by J. Ribbens.
# Reconfirmed for OpenBSD 3.3 by Zachary Hamm, for 3.4 by Jason Ish.
- OpenBSD/2.* | OpenBSD/3.[0123456789])
+ OpenBSD/2.* | OpenBSD/3.[0123456789] | OpenBSD/4.[0])
define_xopen_source=no;;
# On Solaris 2.6, sys/wait.h is inconsistent in the usage
# of union __?sigval. Reported by Stuart Bishop.