Rollup merge of #147233 - GuillaumeGomez:citool-submodule-init, r=Kobzol

Initialize llvm submodule if not already the case to run citool

While working on rust-lang/rust#146414, I ran the following command (to run CI docker locally):

```
cargo run --manifest-path src/ci/citool/Cargo.toml run-local --type pr x86_64-gnu-gcc
```

However, since I didn't have `src/llvm` submodule initialized, it failed. Apparently it's a common issue for people using this tool so this PR removes this small inconvenience.

r? ``@Kobzol``

Author: matthiaskrgr