s390x: fix some fixmes

[folkertdev]

These patterns got some very specific fixes, and so I believe we can rely on them optimizing correctly

• s390x: optimize 128-bit fshl and fshr by high values llvm/llvm-project#154919
• [SystemZ] Allow forming overflow op for i128 llvm/llvm-project#153557

cc @uweigand

There is still a fixme here

#[cfg_attr(test, assert_instr(vacq))]
pub unsafe fn vec_adde_u128(
    a: vector_unsigned_char,
    b: vector_unsigned_char,
    c: vector_unsigned_char,
) -> vector_unsigned_char {
    let a: u128 = transmute(a);
    let b: u128 = transmute(b);
    let c: u128 = transmute(c);
    // FIXME(llvm) https://github.com/llvm/llvm-project/pull/153557
    //     let (d, _carry) = a.carrying_add(b, c & 1 != 0);
    //     transmute(d)
    transmute(vacq(a, b, c))
}

where the right instruction is not emitted when using carrying_add, probably a missing pattern.

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