When disabling OpenSSL support, nestlex.c still needs stddef.h which is
magically included through the OpenSSL headers otherwise.

--- a/configure.in
+++ b/configure.in
@@ -61,7 +61,7 @@
 AC_CHECK_HEADERS(inttypes.h)
 AC_HEADER_SYS_WAIT
 AC_CHECK_HEADERS(fcntl.h limits.h strings.h sys/param.h sys/ioctl.h sys/time.h syslog.h unistd.h)
-AC_CHECK_HEADERS(pwd.h grp.h stdint.h sys/types.h poll.h sys/poll.h sys/socket.h sys/uio.h sys/stat.h netdb.h sys/un.h)
+AC_CHECK_HEADERS(pwd.h grp.h stddef.h stdint.h sys/types.h poll.h sys/poll.h sys/socket.h sys/uio.h sys/stat.h netdb.h sys/un.h)
 AC_CHECK_HEADERS(pty.h)
 AC_CHECK_HEADERS(netinet/in.h netinet/in_systm.h)
 AC_CHECK_HEADERS(netinet/ip.h, [], [], [AC_INCLUDES_DEFAULT
--- a/config.h.in
+++ b/config.h.in
@@ -189,6 +189,9 @@
 /* Define if you have the <grp.h> header file.  */
 #undef HAVE_GRP_H
 
+/* Define if you have the <stddef.h> header file.  */
+#undef HAVE_STDDEF_H
+
 /* Define if you have the <stdint.h> header file.  */
 #undef HAVE_STDINT_H
 
--- a/sysincludes.h
+++ b/sysincludes.h
@@ -51,6 +51,9 @@
 #if HAVE_SYS_TIME_H
 #include <sys/time.h>	/* select(); OpenBSD: struct timespec */
 #endif
+#if HAVE_STDDEF_H
+#include <stddef.h>
+#endif
 #if HAVE_STDINT_H
 #include <stdint.h>	/* uint8_t */
 #endif