fixing messages_xml.h in cmake, but remain an issue as te global variable...

fixing messages_xml.h in cmake, but remain an issue as te global variable messages_definition_xml comes the wrong way, so dependancies between files are wrong

git-svn-id: http://svn.eurecom.fr/openair4G/trunk@6699 818b1a75-f10b-46b9-bf7c-635c3b92a50f