libxml v2.12 adds compiler deprecation warnings. Pacemaker still uses legacy functions and globals from libxml2 in certain places, including (but possibly not limited to) schemas.c.
Details can be found in CLBZ #5530.
We need to look for any instances of libxml2 legacy code within Pacemaker and replace them with calls to the modern API. Backward compatibility is not a concern because we're already using the modern API in some places. It was released over 20 years ago.