toolchain/gcc/arc-2016.03: Fix building on hosts with gcc 6.x

On attempt to build ARC toolchain on the host with gcc 6.1 I saw the
same failure as described in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69959

This change adds a back-port of the fix from upstream gcc, see
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=233572



Note the fix is already a part of gcc-5.4 and gcc-6.1 so no need for
the same fix for others.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>