linux-user: Add support for a group of 2038 safe syscalls

linux-user: Add support for a group of 2038 safe syscalls

This patch implements functionality for following time64 syscalls:

*clock_getres_time64

     This a year 2038 safe variant of syscall:

     int clock_getres(clockid_t clockid, struct timespec *res)
     --finding the resoultion of a specified clock--
     man page: https://man7.org/linux/man-pages/man2/clock_getres.2.html

*timer_gettime64
*timer_settime64

     These are year 2038 safe variants of syscalls:

     int timer_settime(timer_t timerid, int flags,
                       const struct itimerspec *new_value,
                       struct itimerspec *old_value)
     int timer_gettime(timer_t timerid, struct itimerspec *curr_value)
     --arming/dissarming and fetching state of POSIX per-process timer--
     man page: https://man7.org/linux/man-pages/man2/timer_settime.2.html

*timerfd_gettime64
*timerfd_settime64

     These are year 2038 safe variants of syscalls:

     int timerfd_settime(int fd, int flags,
                         const struct itimerspec *new_value,
                         struct itimerspec *old_value)
     int timerfd_gettime(int fd, struct itimerspec *curr_value)
     --timers that notify via file descriptor--
     man page: https://man7.org/linux/man-pages/man2/timerfd_settime.2.html

Implementation notes:

     Syscall 'clock_getres_time64' was implemented similarly to 'clock_getres()'.
     The only difference was that for the conversion of 'struct timespec' from
     host to target, function 'host_to_target_timespec64()' was used instead of
     'host_to_target_timespec()'.

     For other syscalls, new functions 'host_to_target_itimerspec64()' and
     'target_to_host_itimerspec64()' were added to convert the value of the
     'struct itimerspec' from host to target and vice versa. A new type
     'struct target__kernel_itimerspec' was added in 'syscall_defs.h'. This
     type was defined with fields which are of the already defined type
     'struct target_timespec'. This new 'struct target__kernel_itimerspec'
     type is used in these new converting functions. These new functions were
     defined similarly to 'host_to_target_itimerspec()' and 'target_to_host_itimerspec()'
     the only difference being that 'target_to_host_timespec64()' and
     'host_to_target_timespec64()' were used.

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200722153421.295411-3-Filip.Bozuta@syrmia.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>