Fix build breakage without openssl.
From upstream: http://bk1.ntp.org/ntp-stable/?PAGE=patch&REV=5497b345z5MNTuNvJWuqPSje25NQTg

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura ntp-4.2.8.orig/configure.ac ntp-4.2.8/configure.ac
--- ntp-4.2.8.orig/configure.ac	2014-12-22 10:16:10.449311393 -0300
+++ ntp-4.2.8/configure.ac	2014-12-22 10:17:30.757215905 -0300
@@ -102,7 +102,7 @@
 enable_nls=no
 LIBOPTS_CHECK_NOBUILD([sntp/libopts])
 
-NTP_ENABLE_LOCAL_LIBEVENT
+NTP_LIBEVENT_CHECK_NOBUILD([2], [sntp/libevent])
 
 NTP_LIBNTP
 
@@ -771,6 +771,10 @@
 
 #### 
 
+AC_CHECK_FUNCS([arc4random_buf])
+
+####
+
 saved_LIBS="$LIBS"
 LIBS="$LIBS $LDADD_LIBNTP"
 AC_CHECK_FUNCS([daemon])
diff -Nura ntp-4.2.8.orig/libntp/ntp_crypto_rnd.c ntp-4.2.8/libntp/ntp_crypto_rnd.c
--- ntp-4.2.8.orig/libntp/ntp_crypto_rnd.c	2014-12-22 10:16:10.430301237 -0300
+++ ntp-4.2.8/libntp/ntp_crypto_rnd.c	2014-12-22 10:18:04.921468163 -0300
@@ -24,6 +24,21 @@
 int crypto_rand_init = 0;
 #endif
 
+#ifndef HAVE_ARC4RANDOM_BUF
+static void
+arc4random_buf(void *buf, size_t nbytes);
+
+void
+evutil_secure_rng_get_bytes(void *buf, size_t nbytes);
+
+static void
+arc4random_buf(void *buf, size_t nbytes)
+{
+	evutil_secure_rng_get_bytes(buf, nbytes);
+	return;
+}
+#endif
+
 /*
  * As of late 2014, here's how we plan to provide cryptographic-quality
  * random numbers:
diff -Nura ntp-4.2.8.orig/Makefile.am ntp-4.2.8/Makefile.am
--- ntp-4.2.8.orig/Makefile.am	2014-12-22 10:16:10.441307117 -0300
+++ ntp-4.2.8/Makefile.am	2014-12-22 10:16:49.403122474 -0300
@@ -3,6 +3,7 @@
 NULL =
 
 SUBDIRS =		\
+	sntp		\
 	scripts		\
 	include		\
 	libntp		\
@@ -17,7 +18,6 @@
 	clockstuff	\
 	kernel		\
 	util		\
-	sntp		\
 	tests		\
 	$(NULL)
 
@@ -64,7 +64,6 @@
 	.gcc-warning			\
 	libtool				\
 	html/.datecheck			\
-	sntp/built-sources-only		\
 	$(srcdir)/COPYRIGHT		\
 	$(srcdir)/.checkChangeLog	\
 	$(NULL)
diff -Nura ntp-4.2.8.orig/sntp/configure.ac ntp-4.2.8/sntp/configure.ac
--- ntp-4.2.8.orig/sntp/configure.ac	2014-12-22 10:16:10.428300168 -0300
+++ ntp-4.2.8/sntp/configure.ac	2014-12-22 10:24:11.238172928 -0300
@@ -97,11 +97,14 @@
 enable_nls=no
 LIBOPTS_CHECK
 
-AM_COND_IF(
-    [BUILD_SNTP],
-    [NTP_LIBEVENT_CHECK],
-    [NTP_LIBEVENT_CHECK_NOBUILD]
-)
+# From when we only used libevent for sntp:
+#AM_COND_IF(
+#    [BUILD_SNTP],
+#    [NTP_LIBEVENT_CHECK],
+#    [NTP_LIBEVENT_CHECK_NOBUILD]
+#)
+
+NTP_LIBEVENT_CHECK([2])
 
 # Checks for libraries.
 
diff -Nura ntp-4.2.8.orig/sntp/m4/ntp_libevent.m4 ntp-4.2.8/sntp/m4/ntp_libevent.m4
--- ntp-4.2.8.orig/sntp/m4/ntp_libevent.m4	2014-12-22 10:16:10.417294288 -0300
+++ ntp-4.2.8/sntp/m4/ntp_libevent.m4	2014-12-22 10:20:31.757915561 -0300
@@ -1,4 +1,25 @@
-dnl NTP_ENABLE_LOCAL_LIBEVENT				     -*- Autoconf -*-
+# SYNOPSIS						-*- Autoconf -*-
+#
+#  NTP_ENABLE_LOCAL_LIBEVENT
+#  NTP_LIBEVENT_CHECK([MINVERSION [, DIR]])
+#  NTP_LIBEVENT_CHECK_NOBUILD([MINVERSION [, DIR]])
+#
+# DESCRIPTION
+#
+# AUTHOR
+#
+#  Harlan Stenn
+#
+# LICENSE
+#
+#  This file is Copyright (c) 2014 Network Time Foundation
+# 
+#  Copying and distribution of this file, with or without modification, are
+#  permitted in any medium without royalty provided the copyright notice,
+#  author attribution and this notice are preserved.  This file is offered
+#  as-is, without any warranty.
+
+dnl NTP_ENABLE_LOCAL_LIBEVENT
 dnl
 dnl Provide only the --enable-local-libevent command-line option.
 dnl
@@ -29,7 +50,7 @@
 dnl but DO NOT invoke DIR/configure if we are going to use our bundled
 dnl version.  This may be the case for nested packages.
 dnl
-dnl provide --enable-local-libevent .
+dnl provides --enable-local-libevent .
 dnl
 dnl Examples:
 dnl
diff -Nura ntp-4.2.8.orig/util/Makefile.am ntp-4.2.8/util/Makefile.am
--- ntp-4.2.8.orig/util/Makefile.am	2014-12-22 10:16:10.435303910 -0300
+++ ntp-4.2.8/util/Makefile.am	2014-12-22 10:21:02.500339706 -0300
@@ -19,6 +19,7 @@
 LDADD=		../libntp/libntp.a $(LDADD_LIBNTP) $(LIBM) $(PTHREAD_LIBS)
 tg2_LDADD=	../libntp/libntp.a $(LDADD_LIBNTP) $(LIBM)
 ntp_keygen_LDADD  = version.o $(LIBOPTS_LDADD) ../libntp/libntp.a
+ntp_keygen_LDADD += $(LDADD_LIBEVENT)
 ntp_keygen_LDADD += $(LDADD_LIBNTP) $(PTHREAD_LIBS) $(LDADD_NTP) $(LIBM)
 ntp_keygen_SOURCES = ntp-keygen.c ntp-keygen-opts.c ntp-keygen-opts.h