In file included from s390x_gs_threads.c:10:0:
../lib/lock.h: In function 'mutex_lock':
../lib/lock.h:148:4: error: implicit declaration of function 'pr_perror' [-Werror=implicit-function-declaration]
    pr_perror("futex");

Reported-by: Mr Jenkins
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>