[llvm] [CAS] Add MappedFileRegionArena (PR #114099)

[David Spickett via llvm-commits]

DavidSpickett wrote:

(cross posting from Discord)

Tests crashing on armv8 32-bit as well - https://lab.llvm.org/buildbot/#/builders/154/builds/21514

```
--
Note: Google Test filter = CASProgramTest.MappedFileRegionArenaTest
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from CASProgramTest
 #0 0x0ca34e68 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x44e68)
 #1 0x0ca326e8 llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x426e8)
 #2 0x0ca36000 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0xef29d6f0 __default_rt_sa_restorer ./signal/../sysdeps/unix/sysv/linux/arm/sigrestorer.S:80:0
 #4 0x0ca663b0 llvm::cas::MappedFileRegionArena::create(llvm::Twine const&, unsigned long long, unsigned long long, llvm::function_ref<llvm::Error (llvm::cas::MappedFileRegionArena&)>) (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x763b0)
 #5 0x0ca14a38 CASProgramTest_MappedFileRegionArenaTest_Test::TestBody()::$_0::operator()(llvm::StringRef) const ProgramTest.cpp:0:0
 #6 0x0ca14940 CASProgramTest_MappedFileRegionArenaTest_Test::TestBody() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x24940)
 #7 0x0ca82d68 testing::Test::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x92d68)
 #8 0x0ca84084 testing::TestInfo::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x94084)
 #9 0x0ca84ca8 testing::TestSuite::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x94ca8)
#10 0x0ca959b8 testing::internal::UnitTestImpl::RunAllTests() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0xa59b8)
#11 0x0ca94f38 testing::UnitTest::Run() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0xa4f38)
#12 0x0ca6f604 main (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/CAS/CASTests+0x7f604)
#13 0xef28d7d6 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#14 0xef28d886 call_init ./csu/libc-start.c:128:20
#15 0xef28d886 __libc_start_main ./csu/libc-start.c:379:5
../llvm/llvm/unittests/CAS/ProgramTest.cpp:147: Failure
Value of: PI.ReturnCode == 0
  Actual: false
Expected: true
../llvm/llvm/unittests/CAS/ProgramTest.cpp:147
Value of: PI.ReturnCode == 0
  Actual: false
Expected: true
```

Actually I'm not sure this is a "crash" as such, maybe it's just printing the traceback that got it to the assert. Hard to tell.

Going to reproduce it locally.

https://github.com/llvm/llvm-project/pull/114099