cudaPackages_10.cudatoolkit: fix infinite recursion in setupCudaHook

pkgs/development/compilers/cudatoolkit/extension.nix

@@ -59,9 +59,6 @@ final: prev: let
           # Required in addition to ccRoot as otherwise bin/gcc is looked up
           # when building CMakeCUDACompilerId.cu
           substitutions.ccFullPath = "${backendStdenv.cc}/bin/${backendStdenv.cc.targetPrefix}c++";
-
-          # Required by cmake's enable_language(CUDA) to build a test program
-          substitutions.cudartRoot = prev.lib.getDev (final.cuda_cudart or final.cudatoolkit);
         }
         ./hooks/setup-cuda-hook.sh)
     { });

pkgs/development/compilers/cudatoolkit/hooks/nvcc-setup-hook.sh

@@ -0,0 +1,5 @@
+# shellcheck shell=bash
+
+# CMake's enable_language(CUDA) runs a compiler test and it doesn't account for
+# CUDAToolkit_ROOT. We have to help it locate libcudart
+export NVCC_APPEND_FLAGS+=" -L@cudartRoot@/lib -I@cudartRoot@/include"

pkgs/development/compilers/cudatoolkit/redist/overrides.nix

@@ -27,6 +27,11 @@ in
       inherit (prev.backendStdenv) cc;
     in
     {
+      # Required by cmake's enable_language(CUDA) to build a test program
+      # When implementing cross-compilation support: this is
+      # final.pkgs.targetPackages.cudaPackages.cuda_cudart
+      env.cudartRoot = "${prev.lib.getDev final.cuda_cudart}";
+
       # Point NVCC at a compatible compiler
 
       # Desiredata: whenever a package (e.g. magma) adds cuda_nvcc to