Function Perl_sv_insert_flags 

pub unsafe fn Perl_sv_insert_flags(
    my_perl: *mut PerlInterpreter,
    bigstr: *mut SV,
    offset: STRLEN,
    len: STRLEN,
    little: *const c_char,
    littlelen: STRLEN,
    flags: U32,
)

thx shim for crate::Perl_sv_insert_flags.