Windows: rustc_codegen_nvvm fails to load due to missing nvvm64_40_0.dll in PATH

I noticed rustc_codegen_nvvm is yapping on Windows:

error: failed to run custom build command for `vecadd v0.1.0 (F:\Git\github.com\rust-gpu\Rust-CUDA\examples\cuda\vecadd)`

Caused by:
  process didn't exit successfully: `F:\Git\github.com\rust-gpu\Rust-CUDA\target\debug\build\vecadd-06fc7e2d750a3fd2\build-script-build` (exit code: 101)
  --- stdout
  cargo::rerun-if-changed=build.rs
  cargo::rerun-if-changed=kernels
  cargo:rerun-if-changed=F:\Git\github.com\rust-gpu\Rust-CUDA\examples\cuda\vecadd\kernels

  --- stderr
  error: failed to run `rustc` to learn about target-specific information

  Caused by:
    process didn't exit successfully: `sccache C:\Users\steve\scoop\persist\rustup\.rustup\toolchains\nightly-2025-03-02-x86_64-pc-windows-msvc\bin\rustc.exe - --crate-name ___ --print=file-names -Zcodegen-backend=F:\Git\github.com\rust-gpu\Rust-CUDA\target\debug\deps\rustc_codegen_nvvm.dll -Zcrate-attr=feature(register_tool) -Zcrate-attr=register_tool(nvvm_internal) -Zcrate-attr=no_std -Zsaturating_float_casts=false "-Cllvm-args=-arch=compute_61 --override-libm" --target nvptx64-nvidia-cuda --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg -Wwarnings` (exit code: 1)
    --- stderr
    error: couldn't load codegen backend \\?\F:\Git\github.com\rust-gpu\Rust-CUDA\target\debug\deps\rustc_codegen_nvvm.dll: LoadLibraryExW failed: The specified module could not be found. (os error 126) (The specified module could not be found. (os error 126)) (retried 5 times)

Then I noticed nvvm64_40_0.dll maybe missing:

Indeed, adding nvvm folder to the PATH env fixed it:

$env:PATH += ";C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v12.9\nvvm\bin"
PS> cargo build
// just works

Reproduce the failure with cargo build from examples/cuda/vecadd and inspect its build.rs invocation of rustc_codegen_nvvm. Check how the Windows process locates nvvm64_40_0.dll and whether the nvvm/bin PATH workaround is expected. Done means the Windows build loads the backend reliably without an undocumented manual environment change.