Display null bytes in DWARF debug info

Display null bytes in DWARF debug info

binutils/

	PR binutils/14420
	* dwarf.c (process_abbrev_section): Add attribute terminator.
	Warn missing section terminator.
	(get_FORM_name): Special check for 0 value.
	(get_AT_name): Likewise.
	(process_debug_info): Display zero abbrev number.  Check
	attribute terminator.

binutils/testsuite/

	PR binutils/14420
	* binutils-all/i386/compressed-1a.d: Updated.
	* binutils-all/objdump.W: Likewise.
	* binutils-all/readelf.wa: Likewise.
	* binutils-all/x86-64/compressed-1a.d: Likewise.

gas/testsuite/

	PR binutils/14420
	* gas/elf/dwarf2-1.d: Updated.
	* gas/elf/dwarf2-2.d: Likwise.
	* gas/i386/dw2-compress-1.d: Likwise.