One of my previous patches added an unguarded access to
inferior_process_group, which is only defined if
PROCESS_GROUP_TYPE is defined.

#ifdef PROCESS_GROUP_TYPE
/* Process group for us and the inferior.  Saved and restored just like
   {our,inferior}_ttystate.  */
PROCESS_GROUP_TYPE our_process_group;
PROCESS_GROUP_TYPE inferior_process_group;
#endif

This patch should fix it.

-- 
Pedro Alves