The 'debugaltlink_name_len =+ 1' bug reported in PR89136 exposes the fact that
the build-id is not verified for the .gnu_debugaltlink.

Fix both problems.

2019-01-31  Tom de Vries  <tdevries@suse.de>

	PR libbacktrace/89136
	* elf.c (elf_add): Read build-id if with_buildid_data.  Fix
	'debugaltlink_name_len =+ 1'.

From-SVN: r268419