Add PTRACE_SECCOMP_GET_METADATA from Linux 4.16 to sys/ptrace.h.

This patch adds the PTRACE_SECCOMP_GET_METADATA constant from Linux
4.16 to all relevant sys/ptrace.h files.  A type struct
__ptrace_seccomp_metadata, analogous to other such types, is also
added.

Tested for x86_64, and with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): New enum value and macro.
	* sysdeps/unix/sysv/linux/bits/ptrace-shared.h
	(struct __ptrace_seccomp_metadata): New type.
	* sysdeps/unix/sysv/linux/aarch64/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/arm/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/ia64/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/powerpc/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/s390/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/sparc/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/tile/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.
	* sysdeps/unix/sysv/linux/x86/sys/ptrace.h
	(PTRACE_SECCOMP_GET_METADATA): Likewise.

(cherry picked from commit 9320ca88)