bug#64186: Patch: Suppress deprecated '-gdb-set target-async' warning message in gdb-mi.el

[Po Lu]

Wang Diancheng <dianchengwang@gmail.com> writes:

> Hi,
>
> The command "-gdb-set target-async" is deprecated since gdb 7.7, It is
> annoyed that there is a message "Warning: 'set target-async', an alias for
> the command 'set mi-async', is deprecated. Use 'set mi-async'." when gdb
> buffer is ready for command. Following is a patch to suppress that
> warning.
>
> Thanks.

What about versions of GDB earlier than 7.7?  We should detect them, and
use `set mi-async' there.