libcxxrt: Add a stub implementation of __cxa_call_terminate

This function is called by GCC 14 if a destructor invoked during
exception unwinding throws an exception.

Reviewed by: emaste
Obtained from: libcxxrt commit 391a3dcc1054e18c2f0dff4e14d6d79ac95399d7
Differential Revision: https://reviews.freebsd.org/D46004