[RFC] multithreaded bfd?

[DJ Delorie]

> I think it sounds like a good idea. I do think we'll need to do
> something other than mmap the object files for this to work well
> though.

Why?  mmapping allows multiple threads to read/write the objects
without having to keep track of the file pointer, and without having
to allocate local memory to hold them.  Let the OS worry about what to
do when we run low on memory.