This may be more of a general issue not specific to the -rt kernel, but hard to say so far.
Could you please find and attach your build log that shows this issue? The file will be found someplace like:
/var/lib/dkms/nvidia/185.18.36/build/make.log
The numbered directory may be different depending on what version you have installed, but if you poke around it should be somewhere like that.
This may be more of a general issue not specific to the -rt kernel, but hard to say so far.
Could you please find and attach your build log that shows this issue? The file will be found someplace like:
/var/lib/ dkms/nvidia/ 185.18. 36/build/ make.log
The numbered directory may be different depending on what version you have installed, but if you poke around it should be somewhere like that.