[PATCH] Remove all duplicate debug info for DWARF2

[dberlin at redhat dot com (Daniel Berlin)]

This patch will remove all duplicate debug info for DWARF2 as we read
it in.
I currently have it set to only do this if the current language is
C++, as I work out if it will work exactly as is for C, or if i need
to modify it.

With this patch installed, you wil see an amazing reduction in memory
taken to debug DWARF2 applications (At least an order of magnitude).
In fact, on quite a few applications I have, it takes more memory now
to debug STABS than DWARF2!

However, the reason i'm not asking for approval quite yet on this
patch is because I'm pretty sure it won't work in some pathological
cases. The problem is that i haven't been able to make it fail (as
compared to gdb without the duplicate removal) on any of my very
large, hairy, multithreaded, C++ applications. So i'd really
appreciate it if someone can produce applications that break with this
patch installed. That way, I know how to fix it.

--Dan

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