[RFA]: threaded watchpoint test

[Michael Chastain]

> OK.  Unfortunately I don't think this test is conclusive; unix.exp will
> always claim to have hardware watchpoints, and on many systems it does
> not (for instance powerpc-linux).  If that turns out to be true we can
> introduce gdb_has_hardware_watchpoints or something along those lines.

Yeah, I'm a bit leery of "set_board_info gdb,no_hardware_watchpoints"
but it already exists (although not used for that purpose).

I missed something, though:

  if [target_info exists gdb,no_hardware_watchpoints] {
    return 0;
  }

Perhaps there should be an UNSUPPORTED in there before the "return 0":

  unsupported "hardware watchpoints on this target"

Daniel, what do you think?

Michael C