Function libffi_closure_callback 

unsafe extern "C" fn libffi_closure_callback<'tcx>(
    _cif: &ffi_cif,
    _result: &mut c_void,
    _args: *const *const c_void,
    data: &LibffiClosureData<'tcx>,
)

A shim function to intercept calls back from native code into the interpreter via function pointers passed to the native code.

For now this shim only reports that such constructs are not supported by miri. As future improvement we might continue execution in the interpreter here.