[llvm] [CMake] Always define runtimes-test-depends (PR #73629)

[Tom Stellard via llvm-commits]

tstellar wrote:

This fixes the `test-depends` target, which would allow us to re-commit 7f215b1380da49dccbf57da3040a40d25ed898f4.

With the config I was testing in #73610, the `check-runtimes` target still gives an error:

```
[4/5] cd /home/fedora/llvm-project/android-build/runtimes/runtimes-aarch64-linux-and...imes/runtimes-aarch64-linux-android21-bins/ --target check-runtimes --config Release
ninja: error: unknown target 'check-runtimes'
```

This is not a regression, though, the `check-runtimes` target also fails in latest main branch with this config.

https://github.com/llvm/llvm-project/pull/73629