linux: update sys/ptrace.h comments

linux: update sys/ptrace.h comments

* sysdeps/unix/sysv/linux/sys/ptrace.h (__ptrace_request): Add comments
about PTRACE_PEEKSIGINFO, PTRACE_GETSIGMASK, PTRACE_SETSIGMASK, and
PTRACE_SECCOMP_GET_FILTER.  Update comments about PTRACE_SINGLESTEP
and PTRACE_SYSCALL.
* sysdeps/unix/sysv/linux/aarch64/sys/ptrace.h: Likewise.
* sysdeps/unix/sysv/linux/ia64/sys/ptrace.h: Likewise.
* sysdeps/unix/sysv/linux/powerpc/sys/ptrace.h: Likewise.
* sysdeps/unix/sysv/linux/s390/sys/ptrace.h: Likewise.
* sysdeps/unix/sysv/linux/sparc/sys/ptrace.h: Likewise.
* sysdeps/unix/sysv/linux/tile/sys/ptrace.h: Likewise.