* sysdeps/unix/sysv/linux/x86_64/syscall.S: Revert last patch.
* rt/Makefile (tests): Add tst-clock_nanosleep. * rt/tst-clock_nanosleep.c: New file. * posix/Makefile (tests): Add tst-nanosleep. * posix/tst-nanosleep.c: New file.