GDBserver patch for x86 LynxOS-178

[Joel Brobecker <brobecker at adacore dot com>]

Hello,

As I hinted before, I have not been able to build GDBserver since
we switched over to C++, because I don't have a C++ compiler
for that target (I am not giving up yet, though).

So, if you are wondering why I am still submitting a GDBserver
patch for that target, it's because I have been working on x86
LynxOS-178 with GDBserver 7.10, and I think this one is a
straightforward cherry-pick, and will be useful if we manage
to port G++ and the libstdc++ to this target.

In the meantime, the patch was tested on x86-lynx18elf, with
a baseline based on GDB 7.10.

One element I did not explore was the idea of perhaps having
a specific target description xml for this platform, so as to not
show the registers that are not available on LynxOS-178.
In my opinion, it's only a nice-to-have, so I left it for some
other time. I'd like to finish the work on GDBserver for Windows,
for instance.

Thanks,
-- 
Joel