[clang] [llvm] [Clang] Cleanup docs and comments relating to -fextend-variable-liveness (PR #124767)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-aarch64-dylib` running on `linaro-flang-aarch64-dylib` while building `clang,llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/50/builds/9522

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
32.412 [3993/21/2812] Building TestTransformDialectExtensionTypes.h.inc...
32.412 [3993/20/2813] Building TestTilingInterfaceTransformOps.cpp.inc...
32.412 [3993/19/2814] Generating ../../../../share/man/man1/scan-build.1
32.413 [3993/18/2815] Generating ../../../../lib/libscanbuild/compilation.py
32.413 [3993/17/2816] Generating ../../../../lib/libscanbuild/intercept.py
32.413 [3993/16/2817] Generating ../../../../lib/libscanbuild/report.py
32.413 [3993/15/2818] Building TestTilingInterfaceTransformOps.h.inc...
32.414 [3993/14/2819] Building CXX object tools/mlir/tools/tblgen-lsp-server/CMakeFiles/tblgen-lsp-server.dir/tblgen-lsp-server.cpp.o
32.414 [3993/13/2820] Generating ../../../../lib/libscanbuild/resources/scanview.css
32.434 [3993/12/2821] Building Options.inc...
FAILED: tools/clang/include/clang/Driver/Options.inc /home/tcwg-buildbot/worker/flang-aarch64-dylib/build/tools/clang/include/clang/Driver/Options.inc 
cd /home/tcwg-buildbot/worker/flang-aarch64-dylib/build && /home/tcwg-buildbot/worker/flang-aarch64-dylib/build/bin/llvm-tblgen -gen-opt-parser-defs -I /home/tcwg-buildbot/worker/flang-aarch64-dylib/llvm-project/clang/include/clang/Driver -I/home/tcwg-buildbot/worker/flang-aarch64-dylib/llvm-project/clang/include -I/home/tcwg-buildbot/worker/flang-aarch64-dylib/build/tools/clang/include -I/home/tcwg-buildbot/worker/flang-aarch64-dylib/build/include -I/home/tcwg-buildbot/worker/flang-aarch64-dylib/llvm-project/llvm/include /home/tcwg-buildbot/worker/flang-aarch64-dylib/llvm-project/clang/include/clang/Driver/Options.td --write-if-changed -o tools/clang/include/clang/Driver/Options.inc -d tools/clang/include/clang/Driver/Options.inc.d
/home/tcwg-buildbot/worker/flang-aarch64-dylib/llvm-project/clang/include/clang/Driver/Options.td:4356:3: error: Expected comma before next argument
  Values<"all,this,none">,
  ^
32.441 [3993/11/2822] Linking CXX static library lib/libLLVMDlltoolDriver.a
32.441 [3993/10/2823] Linking CXX static library lib/libLLVMInterfaceStub.a
32.443 [3993/9/2824] Linking CXX static library lib/libLLVMLibDriver.a
32.444 [3993/8/2825] Linking CXX static library lib/libLLVMDebugInfoDWARF.a
32.444 [3993/7/2826] Linking CXX static library lib/libLLVMObjCopy.a
32.445 [3993/6/2827] Linking CXX static library lib/libLLVMRuntimeDyld.a
32.446 [3993/5/2828] Linking CXX static library lib/libLLVMXRay.a
32.450 [3993/4/2829] Linking CXX static library lib/libLLVMObjectYAML.a
32.453 [3993/3/2830] Linking CXX static library lib/libLLVMDebugInfoPDB.a
32.458 [3993/2/2831] Linking CXX static library lib/libLLVMJITLink.a
32.651 [3993/1/2832] Linking CXX executable bin/clang-tblgen
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/124767