the aio operations that lead to calling __aio_get_queue with the
possibility to expand the fd map are not AS-safe, but if they are
interrupted by a signal handler, the signal handler may call close,
which is required to be AS-safe. due to __aio_get_queue taking the
write lock without blocking signals, such a call to close from a
signal handler could deadlock.
change __aio_get_queue to block signals if it needs to obtain a write
lock, and restore when finished.
Rich Felker
d8f35e29d0