tools include arch: Grab a copy of x86's prctl.h

We need it to generate the tables for the 'code' arch_prctl's syscall
argument.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-vu890pi18fpd4eyz61cazckj@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>