Change get_debug_info such that it does not build up an absolute
path name. Instead add a function parameter to hold the directory
name, if one was found. Build up the path name when it is needed.
That will come in handy soonish.


git-svn-id: svn://svn.valgrind.org/valgrind/branches/BUF_REMOVAL@14288 a5019735-40e9-0310-863c-91ae7b9d1cf9