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: Arjan van de Ven
Reported-by: Randy Dunlap
Cc: Adrian Hunter
Cc: David Ahern
Cc: Jiri Olsa
Cc: Namhyung Kim
Cc: Wang Nan
Fixes: b31e3e3316a7 ("tools lib api fs: Use str_error_r()")
Link: http://lkml.kernel.org/n/tip-aedt3qzibhnhaov2j4caqi61@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo