Use mmap to create the pthread_internal_t.

Bug: 16847284
Change-Id: I488fa236f57aa3acb29b4ffbbab2fab51b0653be
diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 392e781..c5136c9 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -94,6 +94,8 @@
   char dlerror_buffer[__BIONIC_DLERROR_BUFFER_SIZE];
 };
 
+__LIBC_HIDDEN__ pthread_internal_t* __create_thread_struct();
+__LIBC_HIDDEN__ void __free_thread_struct(pthread_internal_t*);
 __LIBC_HIDDEN__ int __init_thread(pthread_internal_t* thread, bool add_to_thread_list);
 __LIBC_HIDDEN__ void __init_tls(pthread_internal_t* thread);
 __LIBC_HIDDEN__ void __init_alternate_signal_stack(pthread_internal_t*);