libbacktrace: read symbol table of debuginfo file
These become another symbol table to search. This is needed if people
use --strip-all rather than --strip-debug when adding a debuglink
section.
Patch is from GitHub user pickard1.
Fixes https://github.com/ianlancetaylor/libbacktrace/issues/113.
* elf.c (elf_add): Add the symbol table from a debuginfo file.
* Makefile.am (MAKETESTS): Add buildidfull and gnudebuglinkfull
variants of buildid and gnudebuglink tests.
(%_gnudebuglinkfull, %_buildidfull): New patterns.
* Makefile.in: Regenerate.