[libc++abi][NFC] Use C++11 spelling of [[noreturn]] (#207344)

We already use the C++11 spelling for libc++, and there isn't much of a
reason not to use it. Except for the changes in `cxxabi.h` this is even
fully standard code.

GitOrigin-RevId: d6ef81ce4e18563c49116fc82502e4ef237a201d