make: Entering directory `/home/test/autobuild/run/instance-3/buildroot'

Your Buildroot configuration needs a compiler capable of building 32 bits binaries.
If you're running a Debian/Ubuntu distribution, install the g++-multilib package.
For other distributions, refer to their documentation.
make: *** [core-dependencies] Error 1
make: Leaving directory `/home/test/autobuild/run/instance-3/buildroot'