[Coin-lpsolver] Very small fix in CoinSignal for FreeBSD

[Jean-Sebastien Roy]

Hi !

In CoinSignal, FreeBSD is not recognized so the definition of
CoinSighandler_t is given by default and a warning is emitted. I think
the correct version for FreeBSD is:

#if defined(__FreeBSD__)
    typedef sig_t CoinSighandler_t;
#  define CoinSighandler_t_defined
#endif

sig_t is defined in <csignal> through signal.h. See:
http://www.freebsd.org/cgi/man.cgi?query=signal

The other solution (with typeof) should be fine too assuming GNU C.

Regards,

js