Breaking test: Unable to resolve multiple matches for function

When a function is both declared and implemented, doxygenfunction fails with the message:

Warning
doxygenfunction: Unable to resolve multiple matches for function “open_di” with arguments () in doxygen xml output for project “decl_impl” from directory: ../../examples/doxygen/decl_impl/xml/

View example in:
function.html#separated-declaration-implementation-example