Comment 11 for bug 2019160

OK, so the .debug_line entries appear because of

main:
.LFB0:
        .file 1 "t.c"
        .loc 1 1 11

I think I've seen a duplicate bugreport about this where it was suggested
we should apply the remapping when we stream locations. But that also
has effects on diagnostics we emit during LTRANS.

The pragmatic approach with lto-wrapper would still work, but this shows
why a "proper" solution is even more difficult.