Backport of correction for Mac OS X build problem, global variable not
  initiated is "common" and can't be used in shared libraries, unless
  special flags are used (bug#26218)


mysys/my_pthread.c:
  Backport of correction for Mac OS X build problem, global variable not
  initiated is "common" and can't be used in shared libraries, unless
  special flags are used (bug#26218)