std: Use `usleep` temporarily on WASI targets This fixes some fallout from rust-lang/rust#147572 where the `thread::sleep` function is is broken on `wasm32-wasip2` after that PR. The cause for this is a broken implementation of `nanosleep` in wasi-libc itself which is being fixed in WebAssembly/wasi-libc#696. Similar to rust-lang/rust#149864 this avoids the problematic function for now while the wasi-libc changes take some time to propagate into a wasi-sdk release. Closes rust-lang/rust#150290