Fix a number of warnings cropping up on nightly Rust (#2767)

Various small issues here and there, nothing major

cranelift/codegen/src/regalloc/liverange.rs

@@ -66,7 +66,7 @@
 //! Our current implementation uses a sorted array of compressed intervals, represented by their
 //! boundaries (Block, Inst), sorted by Block. This is a simple data structure, enables coalescing of
 //! intervals easily, and shows some nice performance behavior. See
-//! https://github.com/bytecodealliance/cranelift/issues/1084 for benchmarks against using a
+//! <https://github.com/bytecodealliance/cranelift/issues/1084> for benchmarks against using a
 //! bforest::Map<Block, Inst>.
 //!
 //! ## block ordering
@@ -112,7 +112,7 @@
 //! the necessary API to make coalescing easy, nor does it optimize for our types' sizes.
 //!
 //! Even the specialized `bforest::Map<Block, Inst>` implementation is slower than a plain sorted
-//! array, see https://github.com/bytecodealliance/cranelift/issues/1084 for details.
+//! array, see <https://github.com/bytecodealliance/cranelift/issues/1084> for details.
 
 use crate::entity::SparseMapValue;
 use crate::ir::{Block, ExpandedProgramPoint, Inst, Layout, ProgramOrder, ProgramPoint, Value};