[llvm] [openmp] [OpenMP] Allow Fortran tests (PR #150722)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-s390x-linux` running on `systemz-1` while building `llvm,openmp` at step 6 "test-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/16297

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-openmp) failure: test (failure)
******************** TEST 'libomp :: transform/unroll/heuristic_intdo.f90' FAILED ********************
Exit Code: 127

Command Output (stdout):
--
# RUN: at line 3
flang  -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test -L /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src  -fno-omit-frame-pointer -mbackchain -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/ompt -fopenmp  -fopenmp-version=51 /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/unroll/heuristic_intdo.f90 -o /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/unroll/Output/heuristic_intdo.f90.tmp.exe
# executed command: flang -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test -L /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -fno-omit-frame-pointer -mbackchain -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/ompt -fopenmp -fopenmp-version=51 /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/openmp/runtime/test/transform/unroll/heuristic_intdo.f90 -o /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/transform/unroll/Output/heuristic_intdo.f90.tmp.exe
# .---command stderr------------
# | 'flang': command not found
# `-----------------------------
# error: command failed with exit status: 127

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/150722