Run TLS destructors for wasm32-wasip1-threads

The target has support for pthreads and allows
registration of TLS destructors.

library/std/src/sys/thread_local/guard/wasi.rs

@@ -0,0 +1,71 @@
+//! wasm32-wasip1 has pthreads support.
+
+use crate::cell::Cell;
+use crate::sync::atomic::{AtomicBool, Ordering};
+use crate::sys::thread_local::destructors;
+use crate::{ffi, ptr};
+
+// Add a few symbols not in upstream `libc` just yet.
+mod libc {
+    pub use libc::*;
+
+    use crate::ffi;
+
+    #[allow(non_camel_case_types)]
+    pub type pthread_key_t = ffi::c_uint;
+
+    extern "C" {
+        pub fn pthread_key_create(
+            key: *mut pthread_key_t,
+            destructor: unsafe extern "C" fn(*mut ffi::c_void),
+        ) -> ffi::c_int;
+
+        pub fn pthread_setspecific(key: pthread_key_t, value: *const ffi::c_void) -> ffi::c_int;
+    }
+}
+
+pub fn enable() {
+    enable_main();
+    enable_thread();
+}
+
+fn enable_main() {
+    static REGISTERED: AtomicBool = AtomicBool::new(false);
+
+    if !REGISTERED.swap(true, Ordering::AcqRel) {
+        unsafe {
+            assert_eq!(libc::atexit(run_main_dtors), 0);
+        }
+    }
+
+    extern "C" fn run_main_dtors() {
+        unsafe {
+            destructors::run();
+            crate::rt::thread_cleanup();
+        }
+    }
+}
+
+fn enable_thread() {
+    #[thread_local]
+    static REGISTERED: Cell<bool> = Cell::new(false);
+
+    if !REGISTERED.replace(true) {
+        unsafe {
+            let mut key: libc::pthread_key_t = 0;
+            assert_eq!(libc::pthread_key_create(&mut key, run_thread_dtors), 0);
+
+            // We must set the value to a non-NULL pointer value so that
+            // the destructor is run on thread exit. The pointer is only
+            // passed to run_dtors and never dereferenced.
+            assert_eq!(libc::pthread_setspecific(key, ptr::without_provenance(1)), 0);
+        }
+    }
+
+    extern "C" fn run_thread_dtors(_: *mut ffi::c_void) {
+        unsafe {
+            destructors::run();
+            crate::rt::thread_cleanup();
+        }
+    }
+}

library/std/src/sys/thread_local/mod.rs

@@ -85,6 +85,9 @@ pub(crate) mod guard {
         } else if #[cfg(target_os = "windows")] {
             mod windows;
             pub(crate) use windows::enable;
+        } else if #[cfg(all(target_os = "wasi"))] {
+            mod wasi;
+            pub(crate) use wasi::enable;
         } else if #[cfg(any(
             target_family = "wasm",
             target_os = "uefi",