[llvm] [Flang-RT][test] Add flang-rt-mod dependency (PR #201297)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

I re-read the log of a passing build and did a local build (which also passed).
A bit further down the log, I can see this output (which I initially missed, cf. https://lab.llvm.org/buildbot/#/builders/226/builds/8401/steps/7/logs/stdio starting around line 9530)

```
-- The Fortran compiler identification is LLVMFlang 23.0.0
-- Detecting Fortran compiler ABI info
-- Detecting Fortran compiler ABI info - done
-- Check for working Fortran compiler: /home/botworker/bbot/amdgpu-offload-build-only/build/./bin/flang - skipped
-- Fortran support enabled using just-built Flang-RT builtin modules
```

https://github.com/llvm/llvm-project/pull/201297