toolchain-external: Update Synopsys prebuilt toolchain for ARC cores

toolchain-external: Update Synopsys prebuilt toolchain for ARC cores

Sync external prebuilt toolchain with the one we now build in Buildroot,
i.e. arc-2016.09. Since that prebuilt toolchain finally has IPv6 enabled
it works pretty fine for building packages in Buildroot.

Still note:
 1) There might be subtle differences between uClibc configuration
    compared to Buildroot's one.
 2) A couple of patches we apply on top of Builroot-built toolchain
    are obviously missing in the prebuilt version - they will be
    available in the next release.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Vlad Zakharov <vzakhar@synopsys.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>