Linux changes for GDB

[Jim Blandy <jimb@cygnus.com>]

Here's an overview of the Linux changes I've been working on
integrating into Cygnus's sources.  These are not in our main tree
yet, so they aren't appearing in snapshots, but some folks might be
interested in knowing what's coming.

- We have thread support working on Red Hat 5.2, Suse 6.0, and Caldera
  2.2; it may work on others, too.  We do not support Debian yet, but
  once I get my personal machine switched to Debian, that will change.

  This is based on the patch set from Eric Paire, with work by
  H. J. Lu, but with plenty of my own changes and omissions.  So, I am
  responsible for any problems you encounter, not them.

- We have Bill Metzenthen's floating-point patches.  These need to 
  be cleaned up a bit, but with Eli and D.J.'s help, it shouldn't
  take long.

Then there are some bug fixes:
- GDB can step into functions in shared libraries correctly.  On
  Redhat 5.2, at least, you sometimes end up in `strcmp'.  (I need to
  write a test for this one.)
- We can find non-struct return values larger than four bytes
  properly.

Once those are merged, the next major items on my agenda are:
- John Wehle's patches for functions without frame pointers
- H. J.'s fixes for hardware watchpoints