tools lib traceevent: Teach [ce]tags about libtraceeevent error codes

As we use a macro trick to sync each error codes with its description
string, teach [ce]tags to process them properly.

This patch modifies the libtraceevent's Makefile not a kernel one.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-3101nsbg52glxdqih291qj74@git.kernel.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1340352615-20737-1-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>