tools include uapi x86: Grab a copy of unistd.h

In older distros we were not including our copies of unistd_{32,64}.h,
as we were relying on the system's asm/unistd.h, and a log time ago
the files to be included were asm-{x86_64,i386}/unistd.h.

Fix it by also carrying a copy of asm/unistd.h, that will be the same
as in modern distros and will allow us to provide missing __NR_setns,
for instance, in older distros.

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-iwmgm0c4m1ynstktzmkjh8di@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>