Set section vma for COFF in BFD gas [take 2]

[DJ Delorie]

> 2000-06-27 Mark Elbrecht <snowball3@bigfoot.com>
> 
> 	* write.c [BFD_ASSEMBLER && OBJ_COFF && TE_GO32] (set_segment_vma): New.
> 	Set vma and lma for a segment.
> 	(write_object_file) [BFD_ASSEMBLER && OBJ_COFF && TE_GO32]: Use it.

Looks OK to me, but I'll hold off in case others want to comment on
the sanity of such target-specificness.  I do know that cygwin (bfd
gas coff) works right.