Code cleanup.
* charset.c (find_charset_names): Remove variables ix and elt.
Use free_char_ptr_vec.
* elfread.c (build_id_to_debug_filename): New variables debugdir_vec,
back_to and ix. Use dirnames_to_char_ptr_vec. Remove variable
debugdir_end. New variable debugdir_len.
* gdb_vecs.h (free_char_ptr_vec, make_cleanup_free_char_ptr_vec)
(dirnames_to_char_ptr_vec_append, dirnames_to_char_ptr_vec): New
declarations.
* progspace.c (clear_program_space_solib_cache): Remove variables ix
and elt. Use free_char_ptr_vec.
* source.c (add_path): Remove variables argv, arg and argv_index.
New variables dir_vec, back_to, ix and name.
Use dirnames_to_char_ptr_vec_append. Use freeargv instead of
make_cleanup_freeargv. Remove variable separator. Simplify the code
no longer expecting DIRNAME_SEPARATOR.
(openp): Remove variable p, p1 and len. New variables dir_vec,
back_to, ix and dir. Use dirnames_to_char_ptr_vec. Simplify the code
no longer expecting DIRNAME_SEPARATOR.
* symfile.c (find_separate_debug_file): New variables debugdir_vec,
back_to and ix. Use dirnames_to_char_ptr_vec. Remove variable
debugdir_end.
* utils.c (free_char_ptr_vec, do_free_char_ptr_vec)
(make_cleanup_free_char_ptr_vec, dirnames_to_char_ptr_vec_append)
(dirnames_to_char_ptr_vec): New functions.
