* cygthread.cc (cygthread::terminate_thread): Only try to free
	thread stack on systems not freeing it by themselves.
	* wincap.h (wincaps::terminate_thread_frees_stack): New element.
	* wincap.cc: Implement above element throughout.
	* dwarf2read.c (read_cutu_die_from_dwo): New function.
	(lookup_dwo_unit): New function.
	(init_cutu_and_read_dies): Move DWO handling to new functions.