package/log4cxx: add libesmtp optional dependency

libesmtp is an optional dependency (disabled by default) since version
0.10.0 and
https://github.com/apache/logging-log4cxx/commit/8a35b429c6b1bc73635d9b6db482523619199a90

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/log4cxx/log4cxx.mk

@@ -22,4 +22,11 @@ LOG4CXX_CONF_OPTS = \
 
 LOG4CXX_DEPENDENCIES = apr apr-util
 
+ifeq ($(BR2_PACKAGE_LIBESMTP),y)
+LOG4CXX_DEPENDENCIES += libesmtp
+LOG4CXX_CONF_OPTS += --with-SMTP=libesmtp
+else
+LOG4CXX_CONF_OPTS += --without-SMTP
+endif
+
 $(eval $(autotools-package))