I need to use 256bit arithmetic in my C++ code on Mac with arm processor.
According to the accepted answer in this stackoverflow discussion, C++23 has 256bit arithmetic via _BitInt(256) and it has been implemented in Clang-16. I just installed it through brew install llvm and compiling with clang++ outputs

error: unsigned _BitInt of bit sizes greater than 128 not supported.

Am I doing something wrong or is the accepted answer in the above stackoverflow discussion incorrect? (I realize that some of the discussion is about C, but claims are made about C++ as well.)