Add a "fork" of musl as //fusl.

fusl/src/thread/pthread_key_create.c

+#include "pthread_impl.h"
+
+volatile size_t __pthread_tsd_size = sizeof(void *) * PTHREAD_KEYS_MAX;
+void *__pthread_tsd_main[PTHREAD_KEYS_MAX] = { 0 };
+
+static void (*volatile keys[PTHREAD_KEYS_MAX])(void *);
+
+static void nodtor(void *dummy)
+{
+}
+
+int __pthread_key_create(pthread_key_t *k, void (*dtor)(void *))
+{
+        unsigned i = (uintptr_t)&k / 16 % PTHREAD_KEYS_MAX;
+        unsigned j = i;
+        pthread_t self = __pthread_self();
+
+        /* This can only happen in the main thread before
+         * pthread_create has been called. */
+        if (!self->tsd) self->tsd = __pthread_tsd_main;
+
+        if (!dtor) dtor = nodtor;
+        do {
+                if (!a_cas_p(keys+j, 0, (void *)dtor)) {
+                        *k = j;
+                        return 0;
+                }
+        } while ((j=(j+1)%PTHREAD_KEYS_MAX) != i);
+        return EAGAIN;
+}
+
+int __pthread_key_delete(pthread_key_t k)
+{
+        keys[k] = 0;
+        return 0;
+}
+
+void __pthread_tsd_run_dtors()
+{
+        pthread_t self = __pthread_self();
+        int i, j, not_finished = self->tsd_used;
+        for (j=0; not_finished && j<PTHREAD_DESTRUCTOR_ITERATIONS; j++) {
+                not_finished = 0;
+                for (i=0; i<PTHREAD_KEYS_MAX; i++) {
+                        if (self->tsd[i] && keys[i]) {
+                                void *tmp = self->tsd[i];
+                                self->tsd[i] = 0;
+                                keys[i](tmp);
+                                not_finished = 1;
+                        }
+                }
+        }
+}
+
+weak_alias(__pthread_key_delete, pthread_key_delete);
+weak_alias(__pthread_key_create, pthread_key_create);