[llvm] [NFC][LLVM-Tests] Specialize test suite for LLVM unit tests (PR #161442)

[Rahul Joshi via llvm-commits]

jurahul wrote:

Here's the command generated for check-llvm:

```
cd /xyz/llvm-project/build/test && /usr/bin/python3 /xyz/llvm-project/build/./bin/llvm-lit -vv /xyz/llvm-project/build/test
```

So, this will run everything under llvm/test, including the unit tests. Locally I do see several `LLVM-Unit` tests executing when I run `ninja -C build check-llvm`. `check-llvm` is the target that GitHib CI uses. `check-all` is similar.

https://github.com/llvm/llvm-project/pull/161442