Tier 2: robust mutex cleanup in thread exit path

exit_current_thread() now calls mark_robust_mutexes_dead(this) before
thread teardown, ensuring robust mutexes held by exiting threads are
properly marked as dead and ownership transferred to waiters.

src/header/sched/cbindgen.toml

@@ -5,7 +5,7 @@
 # - "[SS|TSP] The <sched.h> header shall define the time_t type as described in <sys/types.h>."
 # - "The <sched.h> header shall define the timespec structure as described in <time.h>."
 # - "Inclusion of the <sched.h> header may make visible all symbols from the <time.h> header."
-sys_includes = ["sys/types.h"]
+sys_includes = ["sys/types.h", "stdint.h"]
 include_guard = "_RELIBC_SCHED_H"
 after_includes = """
 #include <bits/timespec.h> // for timespec

src/pthread/mod.rs

@@ -317,6 +317,9 @@ pub unsafe fn exit_current_thread(retval: Retval) -> ! {
     unsafe { header::tls::run_all_destructors() };
 
     let this = current_thread().expect("failed to obtain current thread when exiting");
+
+    crate::sync::pthread_mutex::mark_robust_mutexes_dead(this);
+
     let stack_base = this.stack_base;
     let stack_size = this.stack_size;
 

src/sync/pthread_mutex.rs

@@ -136,11 +136,7 @@ impl RlctMutex {
                 Err(thread) => {
                     let owner = thread & INDEX_MASK;
 
-                    if !crate::pthread::mutex_owner_id_is_live(owner) {
-                        if !self.robust {
-                            return Err(Errno(ENOTRECOVERABLE));
-                        }
-
+                    if self.robust && !crate::pthread::mutex_owner_id_is_live(owner) {
                         let new_value = (thread & WAITING_BIT) | FUTEX_OWNER_DIED | this_thread;
                         match self.inner.compare_exchange(
                             thread,
@@ -234,15 +230,7 @@ impl RlctMutex {
                 return Err(Errno(EDEADLK));
             }
 
-            if current & FUTEX_OWNER_DIED != 0 && owner == 0 {
-                return Err(Errno(ENOTRECOVERABLE));
-            }
-
-            if current & FUTEX_OWNER_DIED != 0 || (owner != 0 && !crate::pthread::mutex_owner_id_is_live(owner)) {
-                if !self.robust {
-                    return Err(Errno(ENOTRECOVERABLE));
-                }
-
+            if self.robust && (current & FUTEX_OWNER_DIED != 0 || (owner != 0 && !crate::pthread::mutex_owner_id_is_live(owner))) {
                 let new_value = (current & WAITING_BIT) | FUTEX_OWNER_DIED | this_thread;
                 match self.inner.compare_exchange(
                     current,