Auto merge of #57234 - Centril:const-stabilizations-2, r=oli-obk

Const-stabilize `const_int_ops` + `const_ip`

r? @oli-obk

## Note for relnotes: This PR includes https://github.com/rust-lang/rust/pull/57105.

I've added T-lang since this affects intrinsics and the operational semantics of Rust's `const fn` fragment.

## Stable APIs proposed for constification

+ `const_int_ops`:
    + `count_ones`
    + `count_zeros`
    + `leading_zeros`
    + `trailing_zeros`
    + `swap_bytes`
    + `from_be`
    + `from_le`
    + `to_be`
    + `to_le`
+ `const_ip`
    + `Ipv4Addr::new`

## Unstable APIs constified

+ `const_int_conversion`:
    + `reverse_bits`

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/net/ip.rs b/src/libstd/net/ip.rs
index 52a29f4885f..f98113e0896 100644
--- a/src/libstd/net/ip.rs
+++ b/src/libstd/net/ip.rs
@@ -328,7 +328,7 @@ impl Ipv4Addr {
     /// let addr = Ipv4Addr::new(127, 0, 0, 1);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_ip")]
+    #[cfg_attr(stage0, rustc_const_unstable(feature = "const_ip"))]
     pub const fn new(a: u8, b: u8, c: u8, d: u8) -> Ipv4Addr {
         Ipv4Addr {
             inner: c::in_addr {