Python bindings: warnings in generated code causes build failure

Python bindings: warnings in generated code causes build failure

Swig regularily introduces new warnings in the generated code which
makes it difficult to maintain a buildable tree with -Werror. The option
is disabled for this sub-project.

The warnings that appear in the code generated by the current version of
Swig (4.1.0) are also silenced.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I008de07f67b2ce6ebedcf138de5a68c87d869af2