package/gauche: force to use internal libatomic_ops

Force to use internal libatomic_ops of gauche, since the external
libatomic_ops packaged in Buildroot is not compatible with gauche.

Fixes:

  http://autobuild.buildroot.org/results/a97/a979f6a58f0fbb1896830461d6c384f4a65c9429/



[Thomas: tweak commit log.]

Signed-off-by: Hiroshi Kawashima <kei-k@ca2.so-net.ne.jp>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>