Fix -Wshadow warnings in dwarf2.c (seen on alpha-tru64)

[Nick Clifton]

Hi Joel,

> 2010-01-01  Joel Brobecker  <brobecker@adacore.com>
> 
>         Fix -Wshadow warnings in dwarf2.c (seen on alpha-tru64).
>         * dwarf2.c (concat_filename): Rename dirname with dir_name
>         to void shadowing the dirname function.
>         Rename subdirname with subdir_name to stay consistent with
>         the new dir_name variable name.
> 
> OK to apply?

Approved - please apply.

Cheers
   Nick