Thanks to loqs, there is a patch for driver 435.21 and kernel 5.4-rc, at http://ix.io/1MRE .

I have tested this with 5.4-rc2, and it now compiles successfully:

.....................................
WARNING: module nvidia uses symbol filp_open from namespace /NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-drm/nvidia-drm-gem-user-memory.o: $(deps_/home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-drm/nvidia-drm-gem-user-memory.o), but does not import it.
WARNING: module nvidia uses symbol cpufreq_get from namespace VIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-drm/nvidia-drm-gem-user-memory.o: $(deps_/home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-drm/nvidia-drm-gem-user-memory.o), but does not import it.
CC [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-drm.mod.o
LD [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-drm.ko
CC [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-modeset.mod.o
LD [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-modeset.ko
CC [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-uvm.mod.o
LD [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia-uvm.ko
CC [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia.mod.o
LD [M] /home/rgadsdon/kernel/NVIDIA-Linux-x86_64-435.21-54rc2/kernel/nvidia.ko
make[1]: Leaving directory '/usr/src/linux-5.4-rc2'

Robert Gadsdon.   October 7th 2019.
(apologies to loqs  – I should have noticed that this was included in his comment on my 5.4-rc1 article..)