PR29948, heap-buffer-overflow in display_debug_lines_decoded

PR29948, heap-buffer-overflow in display_debug_lines_decoded

This fixes a couple of places in display_debug_lines_decoded that were
off by one in checking DWARF5 .debug_line directory indices.  It also
displays the DWARF5 entry 0 for the program current directory rather
than "." as is done for pre-DWARF5.  I decided against displaying
DW_AT_comp_dir for pre-DWARF5 since I figure it is better for readelf
to minimally interpret debug info.

binutils/
	PR 29948
	* dwarf.c (display_debug_lines_decoded): Display the given
	directory entry 0 for DWARF5.  Properly check directory index
	against number of entries in the table.  Revert to using
	unsigned int for n_directories and associated variables.
	Correct warning messages.
gas/
	* testsuite/gas/elf/dwarf-5-loc0.d: Update.