message: Fix outdated crate names in compiler docs
  Changes `librustc_X` to `rustc_X`, only in documentation comments.
  Plain code comments are left unchanged.
  Also fix incorrect file paths.
diff: //! Codegen vtables and vtable accesses.
  //!
  -//! See librustc_codegen_llvm/meth.rs for reference
  +//! See `rustc_codegen_ssa/src/meth.rs` for reference.
  // FIXME dedup this logic between miri, cg_llvm and cg_clif
  use crate::prelude::*;
  