[Bug bootstrap/81711] New: __res_state is a struct and a function in glibc 2.26

[abominable-snowman at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81711

            Bug ID: 81711
           Summary: __res_state is a struct and a function in glibc 2.26
           Product: gcc
           Version: 6.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: abominable-snowman at yandex dot ru
  Target Milestone: ---

Created attachment 41922
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41922&action=edit
patch to fix

__res_state is a struct and function. Compiler should have
a chance to distinguish ones.

res_state defined as "struct __res_state *" in glibc, so
let's use it.

See resolv/resolv.h:

extern struct __res_state *__res_state(void) __attribute__ ((__const__));

and resolv/bits/types/res_state.h:

struct __res_state {
...
};

typedef struct __res_state *res_state;