Curious as to what this was for I looked at /usr/include/ and only some
python headers define this, and it ends up being to enable "extensions"
on some old OSes:

  /* Enable extensions on AIX 3, Interix */

I guess we can remove this one safely.

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-omnundlxo2brs552bdl6m0j1@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>