gas .file 0 vs. dwarf5

Support added in commit 3417bfca676f for dwarf5 directory table 0
assumed that .file 0 was always the first debug .file directive.
That's not necessarily true.

	* dwarf2dbg.c (get_directory_table_entry): Don't assume entry
        1 is available after putting DW_AT_comp_dir in entry 0.  Pass
	pwd as file0_dirname to recursive call to avoid another
        getpwd in the case file0_dirname is NULL.
1 file changed