Rollup merge of rust-lang#128453 - RalfJung:raw_eq, r=saethlin

raw_eq: using it on bytes with provenance is not UB (outside const-eval)

The current behavior of raw_eq violates provenance monotonicity. See rust-lang#124921 for an explanation of provenance monotonicity. It is violated in raw_eq because comparing bytes without provenance is well-defined, but adding provenance makes the operation UB.

So remove the no-provenance requirement from raw_eq. However, the requirement stays in-place for compile-time invocations of raw_eq, that indeed cannot deal with provenance.

Cc `@rust-lang/opsem`

core/src/intrinsics.rs

@@ -2436,11 +2436,13 @@ extern "rust-intrinsic" {
     ///
     /// # Safety
     ///
-    /// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized or carry a
-    /// pointer value.
+    /// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized.
     /// Note that this is a stricter criterion than just the *values* being
     /// fully-initialized: if `T` has padding, it's UB to call this intrinsic.
     ///
+    /// At compile-time, it is furthermore UB to call this if any of the bytes
+    /// in `*a` or `*b` have provenance.
+    ///
     /// (The implementation is allowed to branch on the results of comparisons,
     /// which is UB if any of their inputs are `undef`.)
     #[rustc_const_unstable(feature = "const_intrinsic_raw_eq", issue = "none")]