Towards nix lib path discovery

[AlexMouton]

The nix package for cuda seems to move files towards use of a singular path structure for all platforms. This seems somewhat reasonable but is surprising when we encounter it as clients. In this PR Ive widened the lib search paths to allow for multiple possible paths per arch/os, and added the nix version the linux search paths.

In nix terms I was born yesterday so if anyone has a better approach Id like to hear it. For this Cuda library specifically I wonder if it would be better to only use the search paths to produce error text and encourage all clients to configure some additional env correctly? Is that already there and Im missing it?

Thanks
A

[tomsmeding]

Most of the changes here are in #79, which I have just merged. The only changes that are not in there seem to be:

• Using cudadevrt as the library name on Linux; it seems to work as-is on plain Linux, and I have a report from a Nix user that my PR was sufficient. Please sound the alarm if you think that is wrong.
• I did not add a shell.nix. Because none of the maintainers of this package use Nix, such a file would only become stale.