Resolve clippy::len_zero

    error: length comparison to one
       --> src/shims/posix/thread.rs:102:12
        |
    102 |         if args.len() < 1 {
        |            ^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `args.is_empty()`
        |
        = note: `-D clippy::len-zero` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#len_zero

Author: dtolnay

src/lib.rs

@@ -17,7 +17,6 @@
     clippy::field_reassign_with_default,
     clippy::from_over_into,
     clippy::if_same_then_else,
-    clippy::len_zero,
     clippy::manual_map,
     clippy::mem_replace_with_default,
     clippy::needless_borrow,

src/shims/posix/thread.rs

@@ -99,7 +99,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
         this.assert_target_os("linux", "prctl");
 
-        if args.len() < 1 {
+        if args.is_empty() {
             throw_ub_format!(
                 "incorrect number of arguments for `prctl`: got {}, expected at least 1",
                 args.len()