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

[NAKAMURA Takumi via llvm-commits]

chapuni wrote:

Could you try again with cleaning unittests?
```
find unittests -type f -name '*.o' | xargs rm
ninja llvm-test-depends # Does it rebuild unittests?
```

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