Namespace the lookup_enum function

Namespace the lookup_enum function

This patch namespaces the lookup_enum function because it causes problem
with the integration in gdb even though it is not exported.
This patch is a first step in the namespacing of the whole internal and
external code base.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>