openntpd: add optional dependency on LibreSSL

OpenNTPD looks for a crypto library with tls_config_set_ca_mem, which
is available in LibreSSL but not OpenSSL. If tls_config_set_ca_mem is
found, crypto support is added to the build.

Because this is not currently checked, crypto support might not be
added due to the order of the build. Add a small check to see if
BR2_PACKAGE_LIBRESSL is selected, and if so, add a dependency for it.

Also add a note about this in the Config.in help section.

Signed-off-by: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/openntpd/Config.in

@@ -9,6 +9,9 @@ config BR2_PACKAGE_OPENNTPD
 	  to remote NTP servers and can act as NTP server itself,
 	  redistributing the local clock. It just works.
 
+	  Crypto support is available if the LibreSSL library is
+	  enabled.
+
 	  http://www.openntpd.org/
 
 comment "openntpd needs a toolchain w/ NPTL"

package/openntpd/openntpd.mk

@@ -11,6 +11,12 @@ OPENNTPD_LICENSE_FILES = COPYING
 # Need to autoreconf for our libtool patch to apply properly
 OPENNTPD_AUTORECONF = YES
 
+# Openntpd searches for tls_config_set_ca_mem which is only available
+# in LibreSSL
+ifeq ($(BR2_PACKAGE_LIBRESSL),y)
+OPENNTPD_DEPENDENCIES += openssl
+endif
+
 # openntpd uses pthread functions for arc4random emulation but forgets
 # to use -pthread
 OPENNTPD_CONF_ENV += CFLAGS="$(TARGET_CFLAGS) -pthread"