find_cuda_helper assumes `lib64` path, but can also be `lib`

[ralfbiedert]

Follow up for #92, just tested this again on NixOS.

The base path is now found when adding cudaPackages.cudatoolkit to the flake's build dependencies, but it then fails because find_cuda_helper's build.rs assumes the CUDA lib path is called lib64, while on Nix the folder inside cudatoolkit is just lib.

[giantcow]

I think this should be okay to close? At least I see some pretty extensive checking here:

Rust-CUDA/crates/cust_raw/build/cuda_sdk.rs

Lines 163 to 195 in afb147e

	fn find_cuda_library_dirs(
	cuda_root: &path::Path,
	) -> Result<Vec<path::PathBuf>, Box<dyn error::Error>> {
	let (target, triple) = Self::parse_target_triple()?;
	assert!(triple.len() >= 3, "Invalid target triple: {:?}", triple);
	let search_dirs = match [triple[0].as_str(), triple[1].as_str(), triple[2].as_str()] {
	["x86_64", "pc", "windows"] => {
	vec![cuda_root.join("lib").join("x64")]
	}
	[_, _, "windows"] => {
	panic!(
	"Cannot support Windows architecture other than \
	x86_64-pc-windows-*. target: {target}"
	);
	}
	[_, _, "linux"] => {
	vec![
	cuda_root.join("lib"),
	cuda_root.join("lib").join("stubs"),
	cuda_root.join("lib64"),
	cuda_root.join("lib64").join("stubs"),
	cuda_root.join("targets").join("x86_64-linux").join("lib"),
	]
	}
	[_, _, _] => {
	panic!("Unsupported target triple: {target}");
	}
	};
	let library_dirs = [Self::parse_cuda_library_path_env(), search_dirs].concat();
	let library_dirs = Self::normalize_dirpaths(library_dirs);
	Ok(library_dirs)
	}