Rollup merge of #93494 - solid-rs:fix-kmc-solid-spawned-task-priority, r=Mark-Simulacrum

kmc-solid: Inherit the calling task's base priority in `Thread::new`

This PR fixes the initial priority calculation of spawned threads on the [`*-kmc-solid_*`](https://doc.rust-lang.org/nightly/rustc/platform-support/kmc-solid.html) Tier 3 targets.

Fixes a spawned task (an RTOS object on top of which threads are implemented for this target; unrelated to async tasks) getting an unexpectedly higher priority if it's spawned by a task whose priority is temporarily boosted by a priority-protection mutex.

Author: matthiaskrgr

library/std/src/sys/itron/thread.rs

@@ -84,10 +84,6 @@ impl Thread {
     ///
     /// See `thread::Builder::spawn_unchecked` for safety requirements.
     pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
-        // Inherit the current task's priority
-        let current_task = task::try_current_task_id().map_err(|e| e.as_io_error())?;
-        let priority = task::try_task_priority(current_task).map_err(|e| e.as_io_error())?;
-
         let inner = Box::new(ThreadInner {
             start: UnsafeCell::new(ManuallyDrop::new(p)),
             lifecycle: AtomicUsize::new(LIFECYCLE_INIT),
@@ -175,7 +171,8 @@ impl Thread {
                 exinf: inner_ptr as abi::EXINF,
                 // The entry point
                 task: Some(trampoline),
-                itskpri: priority,
+                // Inherit the calling task's base priority
+                itskpri: abi::TPRI_SELF,
                 stksz: stack,
                 // Let the kernel allocate the stack,
                 stk: crate::ptr::null_mut(),