pe-i386 object files with .bss sections

[DJ Delorie]

> This gives a problem, when I try to link a gcc generated object file
> (containing a bss section) with the MS linker, since the linker reads
> a bss length of 0.

I think our goal as far as MS compatibility is concerned is to support
MS objects with GNU linker, not the other way around (although that
would be nice too).  We've been slowly fixing the differences as we
go, but we have to be careful not to break backwards compatibility.
Plus, we share a lot of code with the generic COFF bfd, so we have to
be careful about the differences.

> The real fix should distinguish whether we work on an exe or obj
> file. (How?)

See if there's a way to detect if we're doing a PEI bfd (executable)
or a PE bfd (object).