Patch to ld/pe-dll.c: Use explicit lookup for filering excluded objects

[DJ Delorie]

> This all started out by fixing a bug and I've dug myself into a
> stylistic hole as it were.

Rather than digging deeper, let's back up for a moment.  What was the
original bug, and what is the minimum change needed to fix it, given
what we've discussed so far?  We can leave the tables as-is for now,
and simplify them later as a separate change.