solib search algorithm for cross-gdb

[Paul Koning <pkoning at equallogic dot com>]

Currently, the shared library search in solib.c first tries to use the
shared lib filename as given (if solib-absolute-prefix isn't set).

That's exactly right for a native gdb, but it is in general the wrong
answer for a cross-gdb.  If I'm debugging a mips box, or analyzing a
mips corefile, resolving shared lib symbols from intel shared libs in
my /usr/lib is the wrong thing.

.gdbinit helps, but not everyone remembers to do this right every
time.

I was thinking about having the case of "use the filename exactly as
supplied" in solib.c be used only in native gdb.  That seems to
require adding stuff in configure and config.in to tell a native from
a cross build.

I could submit this patch if it sounds like a good feature (otherwise
I'll probably keep it as a private change).  Comments?  Better ways to
do this?

      paul