[llvm] [LV] Add test with BuildVector select condition. (NFC) (PR #207506)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `llvm` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/48041

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

```
Step 6 (test-build-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
...
PASS: Flang :: Transforms/debug-fake-use.fir (4661 of 4671)
PASS: Flang :: Transforms/constant-argument-globalisation.fir (4662 of 4671)
PASS: Flang :: Transforms/OpenACC/acc-implicit-copy-reduction.fir (4663 of 4671)
PASS: Flang :: Transforms/debug-dwarf-version.fir (4664 of 4671)
PASS: Flang :: Transforms/DoConcurrent/multiple_iteration_ranges.f90 (4665 of 4671)
PASS: Flang :: Semantics/modfile72.f90 (4666 of 4671)
PASS: flang-Unit :: Optimizer/./FlangOptimizerTests/165/168 (4667 of 4671)
PASS: Flang :: Transforms/vscale-attr.fir (4668 of 4671)
PASS: Flang :: Driver/linker-options.f90 (4669 of 4671)
PASS: Flang :: Driver/omp-driver-offload.f90 (4670 of 4671)
command timed out: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2388.286529

```

</details>

https://github.com/llvm/llvm-project/pull/207506