While the CLang migration is still ongoing the workaround would be to install libllvm5.0:i386=1:5.0~+rc2-1 libllvm5.0=1:5.0~+rc2-1 from testing. This then allows to install the other packages needed to get GL acceleration working in both 64bit and 32bit applications (like libgl1-mesa-dri:i386).
