[llvm] [CAS] Add OnDiskDataAllocator (PR #161264)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-multistage` running on `ppc64le-clang-multistage-test` while building `llvm` at step 11 "ninja check 2".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/76/builds/13106

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

```
Step 11 (ninja check 2) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
PASS: UBSan-ThreadSanitizer-powerpc64le :: TestCases/ImplicitConversion/signed-integer-truncation-ignorelist.c (102321 of 102330)
PASS: LLVM :: CodeGen/RISCV/attributes.ll (102322 of 102330)
PASS: UBSan-ThreadSanitizer-powerpc64le :: TestCases/ImplicitConversion/unsigned-integer-truncation-ignorelist.c (102323 of 102330)
PASS: Profile-powerpc64le :: Posix/instrprof-value-prof-shared.test (102324 of 102330)
PASS: ThreadSanitizer-powerpc64le :: restore_stack.cpp (102325 of 102330)
PASS: SanitizerCommon-lsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102326 of 102330)
PASS: SanitizerCommon-msan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102327 of 102330)
PASS: SanitizerCommon-tsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102328 of 102330)
PASS: SanitizerCommon-asan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102329 of 102330)
PASS: SanitizerCommon-ubsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102330 of 102330)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=3626.216123

```

</details>

https://github.com/llvm/llvm-project/pull/161264