tools include uapi: Grab a copy of linux/prctl.h

We will use it to generate tables for beautifying prctl's 'option' arg
and some of the others eventually.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-cg8mpmz4hk9nfih685emnbk9@git.kernel.org


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