#630 readelf: stack overflow from DWARF sibling recursion

[Eduardo Santos]

readelf(1) segfaults with

awk 'BEGIN { for (i = 1; i <= 20000; i++) print "int g" i ";" }' >t.c
cc -c -g t.c
(ulimit -s 8192; readelf -w t.o) >/dev/null

because recursion depth scales linearly with sibling chain length. Make recursion depth constant by jumping backward instead.

Do the same for addr2line(1), libdwarf(3), nm(1), and the testsuite.