[patch] Move common macros to i386-common.h

[Joel Brobecker]

> w.r.t this specific patch, its "potential benefit" is that, some
> duplicated functions (i386_length_and_rw_bits, and
> i386_{insert|remove}_aligned_watchpoint) in i386-nat.c and
> gdbserver/i386-low.c can be merged together.  Please take this into account.

Thinking beyond that, I think that GDB should conceptualy contain
a internal GDBserver. That way, when we port GDB to an architecture,
we're pretty much porting GDBserver as well, for free. And when
someone only ported GDBserver at one point, we don't need to redo
that work when porting GDB itself.

-- 
Joel