[clang] [llvm] [MC/DC] Enable nested expressions (PR #125413)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-x86_64-windows` running on `minipc-ryzen-win` while building `clang` at step 8 "test-build-unified-tree-check-flang-rt".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/166/builds/6307

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

```
Step 8 (test-build-unified-tree-check-flang-rt) failure: test (failure)
******************** TEST 'flang-rt-Unit :: Runtime/./RuntimeTests.exe/5/8' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:C:\buildbot\flang-x86_64-windows\build\runtimes\runtimes-bins\flang-rt\unittests\Runtime\.\RuntimeTests.exe-flang-rt-Unit-6848-5-8.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=8 GTEST_SHARD_INDEX=5 C:\buildbot\flang-x86_64-windows\build\runtimes\runtimes-bins\flang-rt\unittests\Runtime\.\RuntimeTests.exe
--

Script:
--
C:\buildbot\flang-x86_64-windows\build\runtimes\runtimes-bins\flang-rt\unittests\Runtime\.\RuntimeTests.exe --gtest_filter=Reductions.InfSums
--
C:/buildbot/flang-x86_64-windows/llvm-project/flang-rt/unittests/Runtime/Reduction.cpp(681): error: Expected equality of these values:
  t1
    Which is: nan
  inf
nan


C:/buildbot/flang-x86_64-windows/llvm-project/flang-rt/unittests/Runtime/Reduction.cpp:681
Expected equality of these values:
  t1
    Which is: nan
  inf
nan



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


```

</details>

https://github.com/llvm/llvm-project/pull/125413