[clang-tools-extra] [libc++] Fix the behavior of throwing `operator new` under -fno-exceptions (PR #69498)

[via cfe-commits]

EricWF wrote:

I'm tempted to just do the non-conforming thing here (because -fno-exceptions is non-conforming), and just assume that when you're building with -fno-exceptions, you're not trying to replace the throwing operator new,  and you'll be fine if we have the throwing kind call the non-throwing kind. 

Is that totally insane?

https://github.com/llvm/llvm-project/pull/69498