If cuda headers are presented to nix in $out/include they are added to future gcc calls via a -isystem flag. However, cuda does not allow kernel calls from template function if these are located in system-headers. We thus move headers from $out/include to $out/usr_include and add a custom hook to add these headers via -I.
Merge pull request #3069 from danielzinn/add_cuda_6

Allowing cuda to use its own thrust library