[clang] [llvm] [ValueTracking] Teach isGuaranteedNotToBeUndefOrPoison about splats (PR #163570)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/38197

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'lld :: ELF/gc-sections-linker-defined-symbol.s' FAILED ********************
Exit Code: 250

Command Output (stdout):
--
# RUN: at line 3
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/llvm-mc -filetype=obj -triple=x86_64-pc-linux /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/lld/test/ELF/gc-sections-linker-defined-symbol.s -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/lld/test/ELF/Output/gc-sections-linker-defined-symbol.s.tmp.o
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/llvm-mc -filetype=obj -triple=x86_64-pc-linux /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/lld/test/ELF/gc-sections-linker-defined-symbol.s -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/lld/test/ELF/Output/gc-sections-linker-defined-symbol.s.tmp.o
# note: command had no output on stdout or stderr
# RUN: at line 4
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/ld.lld /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/lld/test/ELF/Output/gc-sections-linker-defined-symbol.s.tmp.o -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/lld/test/ELF/Output/gc-sections-linker-defined-symbol.s.tmp.so --gc-sections -shared
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/ld.lld /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/lld/test/ELF/Output/gc-sections-linker-defined-symbol.s.tmp.o -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/lld/test/ELF/Output/gc-sections-linker-defined-symbol.s.tmp.so --gc-sections -shared
# .---command stderr------------
# | terminate called after throwing an instance of 'std::system_error'
# |   what():  Resource temporarily unavailable
# `-----------------------------
# error: command failed with exit status: 250

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/163570