<bits/threads_inlines.h>: add missing nullability annotations.

Change-Id: Id98b4011a44e912c5f0da5c91c2be7336a688376
diff --git a/libc/include/bits/threads_inlines.h b/libc/include/bits/threads_inlines.h
index 459866e..05b785a 100644
--- a/libc/include/bits/threads_inlines.h
+++ b/libc/include/bits/threads_inlines.h
@@ -116,13 +116,10 @@
   return __bionic_thrd_error(pthread_mutex_unlock(__mtx));
 }
 
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wnullability-completeness"
 struct __bionic_thrd_data {
-  thrd_start_t __func;
-  void* __arg;
+  thrd_start_t _Nonnull __func;
+  void* _Nullable __arg;
 };
-#pragma clang diagnostic pop
 
 static __inline void* _Nonnull __bionic_thrd_trampoline(void* _Nonnull __arg) {
   struct __bionic_thrd_data __data =