Fix sanitizer build against latest glibc

Summary:
libsanitizer doesn't build against latest glibc anymore, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81066 for details.
One of the changes is that stack_t changed from typedef struct sigaltstack { ... } stack_t; to typedef struct { ... } stack_t; for conformance reasons.
And the other change is that the glibc internal __need_res_state macro is now ignored, so when doing
```
#define __need_res_state
#include <resolv.h>
```
the effect is now the same as just
```
#include <resolv.h>
```
and thus one doesn't get just the
```
struct __res_state { ... };
```
definition, but newly also the
```
extern struct __res_state *__res_state(void) __attribute__ ((__const__));
```
prototype.  So __res_state is no longer a type, but a function.

Reviewers: kcc, ygribov

Reviewed By: kcc

Subscribers: kubamracek

Differential Revision: https://reviews.llvm.org/D35246

llvm-svn: 307969