Uses the arch/x86/ kernel code for x86_64/i386, fallbacking to a gcc
intrinsics implementation that has been tested in at least sparc64.

Will be used for reference counting in tools/perf.

Acked-by: David Ahern <dsahern@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-knfpjowhgyh6x4z0kfuk389j@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

We will need it for atomic.h, so move it from the ad-hoc tools/perf/
place to a tools/ subset of the kernel arch/ hierarchy.

Other aches will follow, each in a cset.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-vy6bqmsvm6puibpay2cy4wid@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>