[compiler-rt] [libunwind] [libunwind][cmake] Compile _Unwind* routines with -fexceptions (PR #121819)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `libunwind-sphinx-docs` running on `gribozavr3` while building `libunwind` at step 3 "Install pip dependencies".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/149/builds/34

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

```
Step 3 (Install pip dependencies) failure: 'pip install -r llvm/docs/requirements-hashed.txt' (failure)
Upon execvpe pip install -r llvm/docs/requirements-hashed.txt ['pip install -r llvm/docs/requirements-hashed.txt'] in environment id 140095679092208
:Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/process.py", line 445, in _fork
    environment)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/process.py", line 523, in _execChild
    os.execvpe(executable, args, environment)
  File "/usr/lib/python2.7/os.py", line 355, in execvpe
    _execvpe(file, args, env)
  File "/usr/lib/python2.7/os.py", line 370, in _execvpe
    func(file, *argrest)
OSError: [Errno 2] No such file or directory

```

</details>

https://github.com/llvm/llvm-project/pull/121819