configure: Fix sysctl.h check for OpenBSD.
diff --git a/configure.ac b/configure.ac
index 5d7dd5c..6dcd72f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -344,7 +344,6 @@
 	sys/statvfs.h \
 	sys/strtio.h \
 	sys/syscall.h \
-	sys/sysctl.h \
 	sys/time.h \
 	sys/times.h \
 	sys/uio.h \
@@ -363,7 +362,7 @@
 
 dnl **** Checks for headers that depend on other ones ****
 
-AC_CHECK_HEADERS([sys/mount.h sys/statfs.h sys/user.h sys/vfs.h],,,
+AC_CHECK_HEADERS([sys/mount.h sys/statfs.h sys/sysctl.h sys/user.h sys/vfs.h],,,
     [#include <sys/types.h>
      #ifdef HAVE_SYS_PARAM_H
      # include <sys/param.h>