S390: Add support for vdso getcpu symbol.

[Adhemerval Zanella]

LGTM.  It could a later clean up to move s390 HAVE_<...>_VSYSCALL to a
common place.

On 04/05/2016 10:15, Stefan Liebler wrote:
> ping
> 
> Any objection? Otherwise, I'll commit this patch.
> 
> On 04/29/2016 09:42 AM, Stefan Liebler wrote:
>> Hi,
>>
>> This patch adds support for symbol __kernel_getcpu in vDSO,
>> which is available with kernel 4.5.
>> Now sched_getcpu is using this symbol if available in mapped vDSO
>> by defining macro HAVE_GETCPU_VSYSCALL. If not available at runtime,
>> the former syscall is used.
>>
>> Bye
>> Stefan
>>
>> ChangeLog:
>>
>>      * sysdeps/unix/sysv/linux/s390/init-first.c:
>>      Add VDSO_SYMBOL(getcpu).
>>      (_libc_vdso_platform_setup): Initialize VDSO_SYMBOL(getcpu).
>>      * sysdeps/unix/sysv/linux/s390/libc-vdso.h:
>>      Add VDSO_SYMBOL(getcpu).
>>      * sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h:
>>      New define HAVE_GETCPU_VSYSCALL.
>>      * sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h: Likewise.
>