get_robust_list.2, get_thread_area.2, getcpu.2, getdents.2, gettid.2, io_cancel.2...

get_robust_list.2, get_thread_area.2, getcpu.2, getdents.2, gettid.2, io_cancel.2, io_destroy.2, io_getevents.2, io_setup.2, io_submit.2, ioprio_set.2, kexec_load.2, llseek.2, modify_ldt.2, mq_getsetattr.2, pivot_root.2, readdir.2, rt_sigqueueinfo.2, set_thread_area.2, sgetmask.2, spu_create.2, spu_run.2, subpage_prot.2, sysctl.2, tkill.2: Add note to SYNOPSIS that there is no glibc wrapper for system call

Reduce the chance that the reader may be misled into thinking
that there is a wrapper function for this system call by noting
explicitly in the SYNOPSIS that there is no glibc wrapper and
pointing the reader to NOTES for further details.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>