[llvm] [ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (PR #86149)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-darwin` running on `doug-worker-3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/2504

<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 'LLVM :: DebugInfo/X86/fake-use.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 6: /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/llc -O2 -filetype=obj -dwarf-linkage-names=Abstract < /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/DebugInfo/X86/fake-use.ll | /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/llvm-dwarfdump --debug-info --debug-line -v - -o /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/test/DebugInfo/X86/Output/fake-use.ll.tmp
+ /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/llc -O2 -filetype=obj -dwarf-linkage-names=Abstract
+ /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/llvm-dwarfdump --debug-info --debug-line -v - -o /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/test/DebugInfo/X86/Output/fake-use.ll.tmp
RUN: at line 7: "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.9/bin/python3.9" /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/DebugInfo/X86/../Inputs/check-fake-use.py /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/test/DebugInfo/X86/Output/fake-use.ll.tmp
+ /Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.9/bin/python3.9 /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/DebugInfo/X86/../Inputs/check-fake-use.py /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/test/DebugInfo/X86/Output/fake-use.ll.tmp
Traceback (most recent call last):
  File "/Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/DebugInfo/X86/../Inputs/check-fake-use.py", line 57, in <module>
    raise RuntimeError(f"Invalid location range list for 'b'")
RuntimeError: Invalid location range list for 'b'

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/86149