[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-solaris11-sparcv9` running on `solaris11-sparcv9` while building `llvm` at step 4 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/13/builds/9911

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

```
Step 4 (build stage 1) failure: 'ninja -j8' (failure)
...
[4546/5839] Linking CXX static library lib/libLLVMDWARFLinkerParallel.a
[4547/5839] Linking CXX static library lib/libLLVMDebugInfoLogicalView.a
[4548/5839] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskCommon.cpp.o
[4549/5839] Linking CXX static library lib/libLLVMDWARFCFIChecker.a
[4550/5839] Linking CXX static library lib/libLLVMDWP.a
[4551/5839] Linking CXX static library lib/libLLVMInterpreter.a
[4552/5839] Linking CXX static library lib/libLLVMXRay.a
[4553/5839] Linking CXX static library lib/libLLVMWindowsManifest.a
[4554/5839] Building CXX object tools/opt/CMakeFiles/LLVMOptDriver.dir/optdriver.cpp.o
[4555/5839] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o
FAILED: lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskDataAllocator.cpp.o 
/opt/llvm/21/bin/clang++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_FILE_OFFSET_BITS=64 -D_GLIBCXX_ASSERTIONS -D_GLIBCXX_USE_CXX11_ABI=1 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/lib/CAS -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/CAS -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include -I/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include/llvm/Support/Solaris -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -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  -O -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -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 /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/CAS/OnDiskDataAllocator.cpp
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/CAS/OnDiskDataAllocator.cpp:212:31: error: no member named 'pointer' in 'llvm::cas::OnDiskDataAllocator'
  212 | Expected<OnDiskDataAllocator::pointer>
      |                               ^~~~~~~
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/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");
      |                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/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 {
      |                                  ^~~~~~~~~
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/include/llvm/CAS/OnDiskDataAllocator.h:29:7: note: OnDiskDataAllocator defined here
   29 | class OnDiskDataAllocator {
      |       ^~~~~~~~~~~~~~~~~~~
3 errors generated.
[4556/5839] Building CXX object tools/opt/CMakeFiles/LLVMOptDriver.dir/NewPMDriver.cpp.o
[4557/5839] Building CXX object utils/PerfectShuffle/CMakeFiles/llvm-PerfectShuffle.dir/PerfectShuffle.cpp.o
[4558/5839] Building CXX object lib/Frontend/OpenACC/CMakeFiles/LLVMFrontendOpenACC.dir/ACC.cpp.o
[4559/5839] Building CXX object lib/CAS/CMakeFiles/LLVMCAS.dir/OnDiskTrieRawHashMap.cpp.o
[4560/5839] Building CXX object lib/Telemetry/CMakeFiles/LLVMTelemetry.dir/Telemetry.cpp.o
[4561/5839] Building CXX object utils/FileCheck/CMakeFiles/FileCheck.dir/FileCheck.cpp.o
[4562/5839] Building CXX object tools/llvm-readobj/CMakeFiles/llvm-readobj.dir/ELFDumper.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

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