[llvm] [PowerPC] Lower ucmp using subtractions (PR #146446)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-quick` running on `linaro-clang-aarch64-quick` while building `llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/23871

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'lit :: timeout-hang.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 18
not env -u FILECHECK_OPTS "/usr/bin/python3.10" /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/timeout-hang/run-nonexistent.txt  --timeout=15 --param external=0 | "/usr/bin/python3.10" /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/timeout-hang.py 5
# executed command: not env -u FILECHECK_OPTS /usr/bin/python3.10 /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/timeout-hang/run-nonexistent.txt --timeout=15 --param external=0
# .---command stderr------------
# | lit.py: /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit/main.py:74: note: The test suite configuration requested an individual test timeout of 0 seconds but a timeout of 15 seconds was requested on the command line. Forcing timeout to be 15 seconds.
# `-----------------------------
# executed command: /usr/bin/python3.10 /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/timeout-hang.py 5
# .---command stdout------------
# | Testing took 6.56s, which is beyond the grace period of 5.0s
# `-----------------------------
# error: command failed with exit status: 1

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/146446