Rollup merge of #136949 - ehuss:wasm-bench-time, r=jhpratt

Fix import in bench for wasm

This import was causing annoying unused import errors when checking the standard library for some wasm targets. The problem is that everything here is disabled if it is wasm32, but this import wasn't cfg'd.

library/std/benches/time.rs

@@ -1,5 +1,3 @@
-use std::time::Instant;
-
 #[cfg(not(target_arch = "wasm32"))]
 use test::{Bencher, black_box};
 
@@ -10,6 +8,7 @@ macro_rules! bench_instant_threaded {
         fn $bench_name(b: &mut Bencher) -> std::thread::Result<()> {
             use std::sync::Arc;
             use std::sync::atomic::{AtomicBool, Ordering};
+            use std::time::Instant;
 
             let running = Arc::new(AtomicBool::new(true));