[libc][stdlib] initial support for __cxa_finalize (#85865)

I'm trying to break up the pieces of supporting __cxa_finalize into smaller
commits. Provide this symbol first, and make use of it from exit.

Next will be to store __dso_handle, then finally to only run callbacks that
were registered from a specific dso.

Link: #85651
Link: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor