Auto merge of #135760 - scottmcm:disjoint-bitor, r=WaffleLapkin

Add `unchecked_disjoint_bitor` per ACP373

Following the names from libs-api in rust-lang/libs-team#373 (comment)

Includes a fallback implementation so this doesn't have to update cg_clif or cg_gcc, and overrides it in cg_llvm to use `or disjoint`, which [is available in LLVM 18](https://releases.llvm.org/18.1.0/docs/LangRef.html#or-instruction) so hopefully we don't need any version checks.

Author: bors

tests/fail/intrinsics/disjoint_bitor.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // one bit in common
+    unsafe { std::intrinsics::disjoint_bitor(0b01101001_u8, 0b10001110) }; //~ ERROR: Undefined Behavior
+}

tests/fail/intrinsics/disjoint_bitor.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: `assume` called with `false`
+  --> tests/fail/intrinsics/disjoint_bitor.rs:LL:CC
+   |
+LL |     unsafe { std::intrinsics::disjoint_bitor(0b01101001_u8, 0b10001110) };
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `assume` called with `false`
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `main` at tests/fail/intrinsics/disjoint_bitor.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+