Rollup merge of #125800 - fortanix:raoul/rte-99-fix_mut_static_task_queue, r=jethrogb

Fix `mut` static task queue in SGX target

[PR 125046](https://github.com/rust-lang/rust/pull/125046) prevents mutable references to statics with `#[linkage]`. Such a construct was used with the tests for the `x86_64-fortanix-unknown-sgx` target. This PR fixes this and cleans up code a bit in 5 steps. Each step passes CI:

- The `mut` static is removed, and `Task` explicitly implements `Send`
- Renaming of the `task_queue::lock` function
- Pass function for `Thread` as `Send` to `Thread::imp` and update when `Packet<'scope, T>` implements `Sync`
- Storing `Task::p` as a type that implements `Send`
- Letting the compiler auto implement `Send` for `Task`

cc: ``@jethrogb``

1 files changed, 3 insertions, 2 deletions

diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index 22215873933..83e27dfb746 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -561,7 +561,8 @@ impl Builder {
         let main = Box::new(main);
         // SAFETY: dynamic size and alignment of the Box remain the same. See below for why the
         // lifetime change is justified.
-        let main = unsafe { Box::from_raw(Box::into_raw(main) as *mut (dyn FnOnce() + 'static)) };
+        let main =
+            unsafe { Box::from_raw(Box::into_raw(main) as *mut (dyn FnOnce() + Send + 'static)) };
 
         Ok(JoinInner {
             // SAFETY:
@@ -1544,7 +1545,7 @@ struct Packet<'scope, T> {
 // The type `T` should already always be Send (otherwise the thread could not
 // have been created) and the Packet is Sync because all access to the
 // `UnsafeCell` synchronized (by the `join()` boundary), and `ScopeData` is Sync.
-unsafe impl<'scope, T: Sync> Sync for Packet<'scope, T> {}
+unsafe impl<'scope, T: Send> Sync for Packet<'scope, T> {}
 
 impl<'scope, T> Drop for Packet<'scope, T> {
     fn drop(&mut self) {