It remains the intention that libpsx be an optional linkage to help an application observe a process wide common security context. However, for
backward compatibility this is not required.

Unfortunately, the fact libcap/cap_proc.c includes a reference to the psx header file, some build environments automatically force this library to be linked.

I think the resolution is to locally introduce the prototype for the affected function in cap_proc.c and not rely on the libpsx header.