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

[via llvm-commits]

https://github.com/EricWF commented:

Are there tests that we actually correctly call the overridden throwing version from the overridden non-throwing version? 

Also, I wonder how much we really care about the library being built without exceptions vs allowing the library to be used without exceptions. 


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