(stdio_file_write_async_safe): New function.
(struct stdio_file): New member fd.
(stdio_file_new): Initialize to_write_async_safe, fd.
(stdio_file_write_async_safe): New function.
(struct stdio_file): New member fd.
(stdio_file_new): Initialize to_write_async_safe, fd.
* ui-file.h (ui_file_write_async_safe_ftype): New typedef.
(set_ui_file_write_async_safe): Declare.
(ui_file_write_async_safe): Declare.
* ui-file.h (ui_file_write_async_safe_ftype): New typedef.
(set_ui_file_write_async_safe): Declare.
(ui_file_write_async_safe): Declare.