Dwarf2 maybe broken in the last two weeks on mainline on MinGW

[Aaron W. LaFramboise]

Something in the last week or two has changed that makes me unable to
debug cc1.  When loading the cc1 executable in gdb, I get this error:

Dwarf Error: bad offset (0x122eed7) in compilation unit header (offset
0x6e9ece + 6) [in module
/aaronwl/cs/env/mingw-head-head-head-20040920/libexec/gcc/i686-pc-mingw32/4.0.0/cc1.exe]

Does anyone have any idea what might have caused this?  I suppose its
possible that there was a latent problem with dwarf2 generation and some
unrelated change broke it.

I'm not entirely sure how to debug this sort of thing, or even how I'd
file a PR for it.  Anyone have any hints?

Aaron W. LaFramboise