Hi,

This is the second iteration of the patch to do some sharing of ptrace 
and native linux stuff between GDB and gdbserver.

I've included fixes based on reviews, so hopefully this is in better 
shape now.

This patch also breaks the shared native linux code into more meaningful 
modules, stored inside the new subdirectory gdb/nat.

Configure and Makefile bits have been updated. The configure bits have 
been adjusted to define PTRACE_TYPE_ARG4 for GDB as well, since this was 
defined for gdbserver already.

Testsuite looks clean, as well as a build with --enable-targets=all and 
--enable-64-bit-bfd.

I decided not to go with a more elegant solution to the config/* changes 
in this patch since it seems to be outside the scope of this work. We 
can probably address that via a different patch set.

Thoughts?

Luis