I'm not sure how this happens, exactly, but your build log shows dkms trying to build with 32-bit options (-m32 -march=i686) but using -mcmodel=kernel, which gives the complaint you saw.
I'm not sure how this happens, exactly, but your build log shows dkms trying to build with 32-bit options (-m32 -march=i686) but using -mcmodel=kernel, which gives the complaint you saw.