[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 `llvm-x86_64-debian-dylib` running on `gribozavr4` while building `clang,llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/60/builds/18238

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
10.694 [6176/96/887] Copying clang's avx10_2convertintrin.h...
10.696 [6175/96/888] Copying clang's avx10_2_512niintrin.h...
10.697 [6174/96/889] Copying clang's avx10_2copyintrin.h...
10.699 [6173/96/890] Building SystemZGenAsmMatcher.inc...
10.701 [6172/96/891] Copying clang's avx10_2_512satcvtdsintrin.h...
10.702 [6171/96/892] Copying clang's avx10_2minmaxintrin.h...
10.711 [6170/96/893] Copying clang's avx10_2niintrin.h...
10.721 [6169/96/894] Copying clang's avx10_2satcvtdsintrin.h...
10.747 [6168/96/895] Building SystemZGenMCCodeEmitter.inc...
10.767 [6167/96/896] Building Options.inc...
FAILED: tools/clang/include/clang/Driver/Options.inc /b/1/llvm-x86_64-debian-dylib/build/tools/clang/include/clang/Driver/Options.inc 
cd /b/1/llvm-x86_64-debian-dylib/build && /b/1/llvm-x86_64-debian-dylib/build/bin/llvm-tblgen -gen-opt-parser-defs -I /b/1/llvm-x86_64-debian-dylib/llvm-project/clang/include/clang/Driver -I/b/1/llvm-x86_64-debian-dylib/llvm-project/clang/include -I/b/1/llvm-x86_64-debian-dylib/build/tools/clang/include -I/b/1/llvm-x86_64-debian-dylib/build/include -I/b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/include /b/1/llvm-x86_64-debian-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
/b/1/llvm-x86_64-debian-dylib/llvm-project/clang/include/clang/Driver/Options.td:4356:3: error: Expected comma before next argument
  Values<"all,this,none">,
  ^
10.767 [6167/95/897] Linking CXX static library lib/libLLVMARMUtils.a
10.767 [6167/94/898] Copying clang's avx10_2satcvtintrin.h...
10.767 [6167/93/899] Copying clang's avx2intrin.h...
10.767 [6167/92/900] Copying clang's avx512bf16intrin.h...
10.767 [6167/91/901] Copying clang's avx512bitalgintrin.h...
10.788 [6167/90/902] Copying clang's avx512bwintrin.h...
10.791 [6167/89/903] Building SystemZGenDisassemblerTables.inc...
10.800 [6167/88/904] Building AArch64GenFastISel.inc...
10.846 [6167/87/905] Building WebAssemblyGenAsmWriter.inc...
10.881 [6167/86/906] Building WebAssemblyGenDisassemblerTables.inc...
10.919 [6167/85/907] Building SPIRVGenTables.inc...
10.947 [6167/84/908] Building WebAssemblyGenRegisterInfo.inc...
10.958 [6167/83/909] Building WebAssemblyGenAsmMatcher.inc...
11.113 [6167/82/910] Building PPCGenFastISel.inc...
11.234 [6167/81/911] Building WebAssemblyGenMCCodeEmitter.inc...
11.250 [6167/80/912] Building VEGenRegisterInfo.inc...
11.294 [6167/79/913] Building RISCVTargetParserDef.inc...
11.342 [6167/78/914] Building WebAssemblyGenDAGISel.inc...
11.395 [6167/77/915] Building XCoreGenCallingConv.inc...
11.413 [6167/76/916] Building WebAssemblyGenSubtargetInfo.inc...
11.478 [6167/75/917] Building VEGenAsmMatcher.inc...
11.490 [6167/74/918] Building XCoreGenAsmWriter.inc...
11.538 [6167/73/919] Building WebAssemblyGenFastISel.inc...
11.593 [6167/72/920] Building XCoreGenDisassemblerTables.inc...
11.678 [6167/71/921] Building XCoreGenRegisterInfo.inc...
11.811 [6167/70/922] Building XCoreGenDAGISel.inc...
11.821 [6167/69/923] Building VEGenAsmWriter.inc...
11.826 [6167/68/924] Building WebAssemblyGenInstrInfo.inc...
11.870 [6167/67/925] Building XCoreGenSubtargetInfo.inc...
11.923 [6167/66/926] Building XCoreGenInstrInfo.inc...
11.940 [6167/65/927] Building VEGenDisassemblerTables.inc...
11.979 [6167/64/928] Building VEGenSubtargetInfo.inc...
11.983 [6167/63/929] Building PPCGenDAGISel.inc...
12.123 [6167/62/930] Building AArch64GenGlobalISel.inc...

```

</details>

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