linux/x86: sync sys/ptrace.h with Linux 4.14 [BZ #22433]

Clone generic linux/sys/ptrace.h, add the following x86-specific
__ptrace_request constants: PTRACE_GET_THREAD_AREA,
PTRACE_SET_THREAD_AREA, PTRACE_ARCH_PRCTL, PTRACE_SYSEMU,
PTRACE_SYSEMU_SINGLESTEP, and PTRACE_SINGLEBLOCK.

[BZ #22433]
* sysdeps/unix/sysv/linux/x86/sys/ptrace.h: New file.