[ping] couple of fixes

[Eric Botcazou]

Unwind/debug info on x86-64/Windows:
  http://gcc.gnu.org/ml/gcc-patches/2012-10/msg00013.html

PR bootstrap/54820 (stage #1 bootstrap failure)
  http://gcc.gnu.org/ml/gcc-patches/2012-10/msg01093.html

-- 
Eric Botcazou