tools lib api: Respect CROSS_COMPILE for the linker

This fixes cross compilation of libapi.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: kernel@pengutronix.de
Cc: patchwork-lst@pengutronix.de
Link: http://lkml.kernel.org/r/1458235670-27341-1-git-send-email-l.stach@pengutronix.de


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