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

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

> Hi, the AIX bot was not building `ProgramTest.cpp` until [00dc72f](https://github.com/llvm/llvm-project/commit/00dc72fa1f328ae52554c5d404460de7381cb7f7) (thanks for the fix!), and we are now observing the following issue (https://lab.llvm.org/buildbot/#/builders/64/builds/5822/steps/6/logs/stdio):
> 
> ```
> FAILED: [code=1] unittests/CAS/CMakeFiles/CASTests.dir/ProgramTest.cpp.o 
> /home/llvm/llvm-external-buildbots/clang.20.1.7/bin/clang++ -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_STATIC -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/unittests/CAS -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/unittests/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 -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/third-party/unittest/googletest/include -I/home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/third-party/unittest/googlemock/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  -Wno-variadic-macros -Wno-gnu-zero-variadic-macro-arguments -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -pthread -Wno-suggest-override -MD -MT unittests/CAS/CMakeFiles/CASTests.dir/ProgramTest.cpp.o -MF unittests/CAS/CMakeFiles/CASTests.dir/ProgramTest.cpp.o.d -o unittests/CAS/CMakeFiles/CASTests.dir/ProgramTest.cpp.o -c /home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/unittests/CAS/ProgramTest.cpp
> /home/llvm/llvm-external-buildbots/workers/aix-ppc64/clang-ppc64-aix/llvm-project/llvm/unittests/CAS/ProgramTest.cpp:30:13: error: unused variable 'ProgramID' [-Werror,-Wunused-variable]
>    30 | static char ProgramID = 0;
>       |             ^~~~~~~~~
> 1 error generated.
> ```

Fix: https://github.com/llvm/llvm-project/pull/159594

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