Because it uses that function, which would lead every tool using it
to need to link against tools/lib/str_error_r.o.

This fixes building tools/vm/, that links with libapi.
Reported-by: NArjan van de Ven <arjan@linux.intel.com>
Reported-by: NRandy Dunlap <rdunlap@infradead.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>
Fixes: b31e3e33 ("tools lib api fs: Use str_error_r()")
Link: http://lkml.kernel.org/n/tip-aedt3qzibhnhaov2j4caqi61@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>