Mqfilter is built if possible

The mqfilter was not built by default even though it should have been. This has
been fixed but the filter is built only if librabbitmq is found. This was done
to avoid having the librabbitmq and its development headers as a hard
dependency.

cmake/macros.cmake

@@ -57,7 +57,7 @@ macro(set_variables)
   set(STATIC_EMBEDDED TRUE CACHE BOOL "Use static version of libmysqld")
 
   # Build RabbitMQ components
-  set(BUILD_RABBITMQ FALSE CACHE BOOL "Build RabbitMQ components")
+  set(BUILD_RABBITMQ TRUE CACHE BOOL "Build RabbitMQ components")
 
   # Build the binlog router
   set(BUILD_BINLOG TRUE CACHE BOOL "Build binlog router")