Function Perl_utf16_to_utf8_base 

pub unsafe fn Perl_utf16_to_utf8_base(
    my_perl: *mut PerlInterpreter,
    p: *mut U8,
    d: *mut U8,
    bytelen: usize,
    newlen: *mut usize,
    high: bool,
    low: bool,
) -> *mut U8

thx shim for crate::Perl_utf16_to_utf8_base.