configure only checks the pkg-config dependencies for activemq when

activemq is enabled. Also check the library dependencies for Kafka
when Kafka is enabled.

configure.ac

@@ -78,20 +78,29 @@ case $target in
         ;;
 esac
 
-PKG_CHECK_MODULES([AMQ], [activemq-cpp])
-PKG_CHECK_MODULES([APR], [apr-1])
-PKG_CHECK_MODULES([APU], [apr-util-1])
-
 # optionally choose the MQ plugins to build, by default all
 AC_ARG_ENABLE([kafka], [AS_HELP_STRING([--enable-kafka],
                        [build the Kafka MQ plugin @<:@default=yes@:>@])],
                        [], [enable_kafka=yes])
 AM_CONDITIONAL([KAFKA_OPT], [test "$enable_kafka" = yes])
+AS_IF([test "x$enable_kafka" != xno],
+      [
+      AC_CHECK_LIB([zookeeper_mt], [zookeeper_init], [],
+                   AC_MSG_ERROR([libzookeeper_mt is required]))
+      AC_CHECK_LIB([rdkafka], [rd_kafka_new], [],
+                   AC_MSG_ERROR([librdkafka is required]))
+      ], [])
 
 AC_ARG_ENABLE([activemq], [AS_HELP_STRING([--enable-activemq],
                           [build the ActiveMQ MQ plugin @<:@default=yes@:>@])],
                           [], [enable_activemq=yes])
 AM_CONDITIONAL([AMQ_OPT], [test "$enable_activemq" = yes])
+AS_IF([test "x$enable_activemq" != xno],
+      [
+      PKG_CHECK_MODULES([AMQ], [activemq-cpp])
+      PKG_CHECK_MODULES([APR], [apr-1])
+      PKG_CHECK_MODULES([APU], [apr-util-1])
+      ], [])
 
 # From Varnish configure.ac
 # Now that we're done using the compiler to look for functions and