4937: Allow overriding rust-analyzer display version r=matklad a=oxalica
The build script invokes `git` for version information which is displayed when rust-analyzer is called with `--version`. But in build environment without `git` or when the source code is not a git repo, there's no way to manually specify the version information.
This patch respects environment variable ~`REV`~ `RUST_ANALYZER_REV` in compile time for overriding.
Related: https://github.com/NixOS/nixpkgs/pull/90976
Co-authored-by: oxalica <oxalicc@pm.me>
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