Add llvm21 to PATH

[tristianc]

I'm using Workbench in a Flatpak, but it doesn't compile Rust projects, even though I've granted it the network permission via Flatseal and I've added the extensions that Workbench instructed me to:

• org.freedesktop.Sdk.Extension.llvm21
• org.freedesktop.Sdk.Extension.rust-stable

On line 83 of src/Extensions/Extensions.js, the version of LLVM used to compile Rust projects is set to llvm21. However, the script to actually add the LLVM extension to $PATH tries to add llvm11 instead.

Until the fix is committed, a user can add the LLVM extension directory to the flatpak's path via an override:

  flatpak override --user \
    --env=PATH=/usr/lib/sdk/llvm21/bin:/usr/lib/sdk/rust-stable/bin:/app/bin:/usr/bin \
    re.sonny.Workbench

[sonnyp]

Thanks!