tools headers: Add limits.h to access __WORDSIZE

We need to make sure limits.h is included before checking if we can use
__WORDSIZE, do it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-5yfoed4rnsck2n3cwhm9mvth@git.kernel.org


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