PATCH: Make gdbserver use async I/O on Linux

[Daniel Jacobowitz]

The only problem I can think of that this might cause is if F_SETOWN is less
portable than FASYNC.  Apparently you need to do that explicitly on a Linux
target before SIGIO will be sent.

This lets C-c on the host be properly handled, stopping the target.

-- 
Daniel Jacobowitz                           Debian GNU/Linux Developer
Monta Vista Software                              Debian Security Team