Fix ntp-keygen build without OpenSSL

Patch borrowed from Gentoo, originally from upstream
Added --enable-libenvent to config since this version
does not have local libevent support but we need the 
functions from the lib.

Signed-off-by: Armin Kuster <akuster808@gmail.com>

Upstream-Status: Backport

Upstream commit:
http://bk1.ntp.org/ntp-stable/?PAGE=patch&REV=5497b345z5MNTuNvJWuqPSje25NQTg
Gentoo bugzilla: https://bugs.gentoo.org/show_bug.cgi?id=533238

Signed-off-by: Markos Chandras <hwoarang@gentoo.org>

Index: ntp-4.2.6p5/libntp/ntp_random.c
===================================================================
--- ntp-4.2.6p5.orig/libntp/ntp_random.c
+++ ntp-4.2.6p5/libntp/ntp_random.c
@@ -498,6 +498,21 @@ ntp_random( void )
 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
+
 /*
  * ntp_crypto_srandom:
  *
Index: ntp-4.2.6p5/util/Makefile.am
===================================================================
--- ntp-4.2.6p5.orig/util/Makefile.am
+++ ntp-4.2.6p5/util/Makefile.am
@@ -21,6 +21,7 @@ AM_CPPFLAGS= -I$(top_srcdir)/include -I$
 LDADD=		../libntp/libntp.a
 ntp_keygen_SOURCES = ntp-keygen.c ntp-keygen-opts.c ntp-keygen-opts.h
 ntp_keygen_LDADD= version.o $(LIBOPTS_LDADD) ../libntp/libntp.a @LCRYPTO@
+ntp_keygen_LDADD += $(LDADD_LIBEVENT)
 
 ETAGS_ARGS=	Makefile.am
 #EXTRA_DIST=	README TAGS
Index: ntp-4.2.6p5/configure.ac
===================================================================
--- ntp-4.2.6p5.orig/configure.ac
+++ ntp-4.2.6p5/configure.ac
@@ -376,6 +376,8 @@ AC_CHECK_FUNC([openlog], ,
 AC_SEARCH_LIBS([MD5Init], [md5 md])
 AC_CHECK_FUNCS(MD5Init)
 
+AC_CHECK_FUNC([arc4random_buf])
+
 NTP_LINEEDITLIBS
 
 dnl Digital UNIX V4.0 and Solaris 7 have POSIX.1c functions in -lrt
@@ -5205,6 +5207,39 @@ AC_MSG_RESULT([$ntp_use_dev_clockctl])
 
 AC_CHECK_HEADERS([sys/capability.h sys/prctl.h])
 
+AC_MSG_CHECKING([if we have libevent capabilities (libevent)])
+
+case "$ac_cv_header_event2_event-config_h" in
+ yes)
+    case "$host" in
+     *) ntp_have_linuxcaps=yes
+	;;
+    esac
+    ;;
+ *)
+    ntp_have_linuxcaps=no
+    ;;
+esac
+
+AC_ARG_ENABLE(
+    [libevent],
+    [AS_HELP_STRING(
+	[--enable-libevent],
+	[+ Use libevent capabilities for arc4random]
+    )],
+    [ntp_have_libevent=$enableval]
+)
+
+AC_MSG_RESULT([$ntp_have_libevent])
+
+case "$ntp_have_libevent" in
+ yes)
+    AC_DEFINE([HAVE_LIBEVENT], [1],
+	[Do we have libevent capabilities?])
+    LIBS="$LIBS -levent"
+esac
+
+
 AC_MSG_CHECKING([if we have linux capabilities (libcap)])
 
 case "$ac_cv_header_sys_capability_h$ac_cv_header_sys_prctl_h" in