Function Perl_mro_set_private_data 

pub unsafe fn Perl_mro_set_private_data(
    my_perl: *mut PerlInterpreter,
    smeta: *mut mro_meta,
    which: *const mro_alg,
    data: *mut SV,
) -> *mut SV

thx shim for crate::Perl_mro_set_private_data.