toolchain: CodeSourcery AArch64 2014.11 does not contain libatomic

toolchain: CodeSourcery AArch64 2014.11 does not contain libatomic

Fixes build error

output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-amd-linux-gnu/4.9.1/../../../../aarch64-amd-linux-gnu/bin/ld:
 cannot find -latomic

using this defconfig

BR2_aarch64=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64=y
BR2_PACKAGE_OPENSSL=y

libopenssl is only used here as an example: all packages adding -latomic
if BR2_TOOLCHAIN_HAS_LIBATOMIC=y are broken, like dav1d, ffmpeg, gnutls,
kodi and vlc.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>