Removing duplicate DWARF2 info

[Martin v. Loewis]

> When you clean out the build directory, you lose the info.
> You lost the objects too, so what's the problem.
> It's like -frepo, but for debug info instead.

Indeed, yet another repository mechanism. A number of gcc contributors
(including myself) believe that any repository mechanism is inherently
broken, and that it is impossible to have it work in all cases where
it currently works.

Apart from the "multiple build directory" issue, you also have the
"static library issue", where you have enormous problems locating the
repository for object files that live in a .a file.

Regards,
Martin