Hi,


currently there is a problem when debugging a virtual thunk.  That is
a decl with DECL_IGNORED_P.  Currently the line information displayed
in gdb is completely bogus, thus the last line of whatever function
is immediately before the PC of the thunk.

This patch improves the debug experience at least a bit by emitting
at the line number information where the thunk has been defined.
I do not dare to touch anything but dwarf2 debug info, therefore
the patch is a bit awkward.


Bootstrapped and reg-tested on x86_64-pc-linux-gnu.
Is it OK for trunk?


Thanks
Bernd.