toolchain: Bump ARC tools to arc-2016.09-rc1

toolchain: Bump ARC tools to arc-2016.09-rc1

As described at:
4520524ba055706236db9f00dd79f1b2e2e87fde
this commit continues a series of updates of ARC tools.
This time we're updating tools to arc-2016.09-rc1.

This update contains a lot of important fixes, e.g. it fixes:
http://autobuild.buildroot.net/results/4c7/4c77f33c842b37bf28cb931edf1b290e1bf4d93c//
http://autobuild.buildroot.net/results/902/902729a0b98675ad803939e3ecdcf230065a6012//
and other failures.

Other important change is that we also update gdb. Now we are
using gdb 7.12.

This version of gdb requires C++ toolchain support so we add
corresponding dependency to gdb Config.in file.

Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
[Thomas:
 - fix dependency on C++ of gdb, it must use BR2_INSTALL_LIBSTDCPP
 - add comment about the C++ dependency of gdb on ARC.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>