Tentatively apply https://github.com/libcxxrt/libcxxrt/pull/27

This marks cxa_allocate_exception, cxa_free_exception and
__cxa_init_primary_exception noexcept, to ensure compatibility with
libc++'s declarations.

PR: 276104
MFC after: 1 month

(cherry picked from commit 3fb2e045791eb6f003205902cdc4f74702770ec6)