[rfa/threads] Eliminate lin-lwp.c

[Andrew Cagney]

> Er, why are you doing this?  Why isn't it possible to have a separate
> target vector without moving all the code around?

You mean add a "lin-lwp.h" which exports everything so that 
"linux-nat.c" can construct that vector, or conversly have "linux-nat.h" 
export everything so that "lin-lwp.c" can construct the vector?

Bleauh! Such a separation is artifical (although perhaphs the single 
file should be called inf-linux.[hc]).

Andrew