[clang] [llvm] [AllocToken] Fix and clarify -falloc-token-max=0 (PR #168689)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-mlir-rhel-clang` running on `ppc64le-mlir-rhel-test` while building `clang,llvm` at step 6 "test-build-check-mlir-build-only-check-mlir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/33485

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

```
Step 6 (test-build-check-mlir-build-only-check-mlir) failure: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
...
PASS: MLIR :: Dialect/SCF/loop-unroll.mlir (3657 of 3676)
PASS: MLIR-Unit :: IR/./MLIRIRTests/101/130 (3658 of 3676)
PASS: MLIR :: Pass/ir-printing-file-tree.mlir (3659 of 3676)
PASS: MLIR :: mlir-runner/utils.mlir (3660 of 3676)
PASS: MLIR-Unit :: IR/./MLIRIRTests/100/130 (3661 of 3676)
PASS: MLIR :: mlir-runner/simple.mlir (3662 of 3676)
PASS: MLIR :: mlir-tblgen/cpp-class-comments.td (3663 of 3676)
PASS: MLIR :: Pass/pipeline-parsing.mlir (3664 of 3676)
PASS: MLIR :: mlir-tblgen/op-error.td (3665 of 3676)
PASS: MLIR :: Pass/pipeline-options-parsing.mlir (3666 of 3676)
command timed out: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1790.266292

```

</details>

https://github.com/llvm/llvm-project/pull/168689