Fix readelf so it doesn't complain about corrupt attribute.

Fix readelf so it doesn't complain about corrupt attribute.

When a DW_FORM_flag_present attribute comes at the very end of a
debug section, readelf complains about a corrupt attribute
because it's checking to make sure there's at least one byte of
data remaining. This patch suppresses the check when the form
is DW_FORM_flag_present.

2014-02-11  Cary Coutant  <ccoutant@google.com>

	* binutils/dwarf.c (read_and_display_attr_value): Don't warn
	for zero-length attribute value.