Problem: upgrade to vergen 4.0.2 fails to compile

[tomtau]

error[E0609]: no field `llvm_version` on type `VersionMeta`
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Error:   --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/vergen-4.0.2/src/feature/rustc.rs:79:42
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   |
914
79 |             if let Some(llvmver) = rustc.llvm_version {
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   |                                          ^^^^^^^^^^^^ unknown field
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   |
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   = note: available fields are: `semver`, `commit_hash`, `commit_date`, `build_date`, `channel` ... and 2 others