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