[gas] Fix file 0 dir with -gdwarf-5

In out_dir_and_file_list, if file 0 is copied from file 1, only the filename
is copied, and the dir and md5 fields are left to their default values.

Fix this by adding the copy of the dir and md5 fields.

gas/ChangeLog:

2021-11-26  Tom de Vries  <tdevries@suse.de>

	PR 28629
	* dwarf2dbg.c (out_dir_and_file_list): When copying file 1 to file 0,
	also copy dir and md5 fields.
	* testsuite/gas/i386/dwarf5-line-4.d: Adjust expected output.