Apply suggestions from code review

Co-authored-by: Ralf Jung <post@ralfj.de>

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -1164,6 +1164,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
             let params = vec![AbiParam::new(fx.pointer_type); 3];
             let returns = vec![AbiParam::new(types::I32)];
             let args = &[lhs_ptr, rhs_ptr, bytes_val];
+            // Here we assume that the `memcmp` provided by the target is a NOP for size 0.
             let cmp = fx.lib_call("memcmp", params, returns, args)[0];
             ret.write_cvalue(fx, CValue::by_val(cmp, ret.layout()));
         }