* configure.in: always check dladdr(1).

* addr2line.c (fill_lines): show the line number in C backtrace if
  ruby is built without --enable-shared (PIE) on Linux.
  patch is originally by Shinichiro Hamaji
  https://twitter.com/shinh/status/441957774264504321
  NOTE: ld doesn't insert __executable_start for PIE.
  dladdr(3)'s argument must be a function pointer.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45305 b2dd03c8-39d4-4d8f-98ff-823fe69b080e