(fixed patch) pe-dll fix for exporting common symbols

[DJ Delorie]

> Thank you! I believe you just pointed me to the correct fix. The problem 
> is that currently the i386-pe ld is trying to write out the export 
> table in after_open, hence there are actually symbols with 
> bfd_link_hash_common, and things are going haywire. I'll redo it so that 
> it's done in ldemul_finish instead.

You can't build the export table in ldemul_finish because building the
export table produces yet another section that must be linked in (the
reloc section is a mess because of this, but at least it's one of the
last sections in the dll so has less ramifications if its size
changes).  Perhaps just the part about filling in the final values can
be shifted to the later stage?