Removing duplicate DWARF2 info

[Daniel Berlin <dberlin at redhat dot com>]

I know this has been hashed over before, but nobody ever seems to do it
where it needs to be done (I do it in GDB when we load the stuff), and i'm
guessing it's because there are three people on the planet with the
knowledge of how LD works that can make this happen.

Why can't we simply not emit the duplicate info, taking LD out of the
picture completely.
All it seems this would entail is keeping track of what we've emitted info
for, over the course of more than one file. 
Couldn't we have a simple persistent hash table in a file, and do a lookup
in that, then do the check to see if we emitted it during this
compilation?
That doesn't really seem that tricky to do, or am i missing something?