ELF unexec: Merge Alpha and MIPS COFF debug handling

ELF unexec: Merge Alpha and MIPS COFF debug handling

Emacs should build on ppc64el.  A problem with the bss has been fixed.

This upstream patch has been added [3/10]:

  ELF unexec: Merge Alpha and MIPS COFF debug handling

  * unexelf.c (unexec): Merge Alpha and MIPS COFF debug handling.
  Don't find .mdebug section index, find the section in the loop.
  Allow for unlikely possibility that .mdebug is located at sh_offset
  before bss segment, by calculating move from difference in
  sh_offset rather than just assuming new_data2_size.  Simplify
  cbLineOffset handling.

Origin: upstream, commit: 47c6e3035b8182c6436de4673473de7824ad59f1
Bug: http://debbugs.gnu.org/20614
Bug-Debian: http://bugs.debian.org/808347
Added-by: Rob Browning <rlb@defaultvalue.org>