These __need macros are only used internally, by nptl/descr.h.
However, including all of resolv.h from descr.h causes build failures
due to resolv.h's dozens of pseudo-struct-field macros, some of which
collide with struct fields in NPTL internal data structures.
Similarly, including all of list.h from descr.h produces an include
cycle, atomic.h -> atomic-machine.h -> tls.h -> descr.h -> list.h ->
atomic.h, and then list.h tries to use atomic.h macros that haven't
been defined yet. So we do need mini-headers for these. In the
list.h case I called it include/list_t.h since it isn't going to be
installed.
* resolv/resolv.h: Remove __need_res_state logic.
Move definition of res_state and related constants to ...
* resolv/bits/types/res_state.h: ...this new file.
* resolv/Makefile: Install bits/types/res_state.h.
* include/bits/types/res_state.h: New wrapper.
* include/list.h: Remove __need_list_t logic.
Move definition of list_t to ...
* include/list_t.h: ...this new file.
* nptl/descr.h: Include list_t.h and bits/types/res_state.h
instead of list.h and resolv.h.
