[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-ppc64-aix` running on `aix-ppc64` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/64/builds/6021

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
4894.106 [456/10/5047] Linking CXX static library lib/libLLVMDebugInfoLogicalView.a
4894.179 [455/10/5048] Linking CXX static library lib/libLLVMDWARFCFIChecker.a
4894.239 [454/10/5049] Linking CXX static library lib/libLLVMDWP.a
4894.293 [453/10/5050] Linking CXX static library lib/libLLVMAMDGPUTargetMCA.a
4894.351 [452/10/5051] Linking CXX static library lib/libLLVMRISCVTargetMCA.a
4894.404 [451/10/5052] Linking CXX static library lib/libLLVMX86TargetMCA.a
4894.665 [450/10/5053] Building CXX object lib/Support/LSP/CMakeFiles/LLVMSupportLSP.dir/Transport.cpp.o
4894.723 [449/10/5054] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/InMemoryCAS.cpp.o
4895.130 [448/10/5055] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/MappedFileRegionArena.cpp.o
4895.398 [447/10/5056] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o
FAILED: [code=1] lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o 
/home/llvm/llvm-external-buildbots/clang.20.1.7/bin/clang++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LARGE_FILE_API -D_XOPEN_SOURCE=700 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/build/lib/CAS -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/lib/CAS -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/build/include -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/include -pthread -mcmodel=large -fPIC -Werror -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -pthread -MD -MT lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o -MF lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o.d -o lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o -c /home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/lib/CAS/OnDiskDataAllocator.cpp
/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/lib/CAS/OnDiskDataAllocator.cpp:212:31: error: no member named 'pointer' in 'llvm::cas::OnDiskDataAllocator'
  212 | Expected<OnDiskDataAllocator::pointer>
      |          ~~~~~~~~~~~~~~~~~~~~~^
/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/lib/CAS/OnDiskDataAllocator.cpp:214:10: error: no viable conversion from returned value of type 'Error' to function return type 'int'
  214 |   return createStringError(make_error_code(std::errc::not_supported),
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  215 |                            "OnDiskDataAllocator is not supported");
      |                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/lib/CAS/OnDiskDataAllocator.cpp:218:34: error: out-of-line definition of 'beginData' does not match any declaration in 'llvm::cas::OnDiskDataAllocator'
  218 | const char *OnDiskDataAllocator::beginData(FileOffset Offset) const {
      |                                  ^~~~~~~~~
/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/include/llvm/CAS/OnDiskDataAllocator.h:29:7: note: OnDiskDataAllocator defined here
   29 | class OnDiskDataAllocator {
      |       ^~~~~~~~~~~~~~~~~~~
3 errors generated.
4895.446 [447/9/5057] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/ObjectStore.cpp.o
4896.139 [447/8/5058] Building CXX object lib/Frontend/OpenACC/CMakeFiles/LLVMFrontendOpenACC.dir/ACC.cpp.o
4896.552 [447/7/5059] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskTrieRawHashMap.cpp.o
4896.712 [447/6/5060] Building CXX object lib/WindowsManifest/CMakeFiles/LLVMWindowsManifest.dir/WindowsManifestMerger.cpp.o
4897.192 [447/5/5061] Building CXX object utils/PerfectShuffle/CMakeFiles/llvm-PerfectShuffle.dir/PerfectShuffle.cpp.o
4897.320 [447/4/5062] Building CXX object lib/Telemetry/CMakeFiles/LLVMTelemetry.dir/Telemetry.cpp.o
4897.603 [447/3/5063] Building CXX object lib/Support/LSP/CMakeFiles/LLVMSupportLSP.dir/Protocol.cpp.o
4899.854 [447/2/5064] Building CXX object utils/yaml-bench/CMakeFiles/yaml-bench.dir/YAMLBench.cpp.o
4900.920 [447/1/5065] Building CXX object utils/UnicodeData/CMakeFiles/UnicodeNameMappingGenerator.dir/UnicodeNameMappingGenerator.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

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