[libc++] Implement P2467R1: Support exclusive mode for fstreams

This patch brings std::ios_base::noreplace from P2467R1 to libc++.
This requires compiling the shared library in C++23 mode since otherwise
fstream::open(...) doesn't know about the new flag.

Differential Revision: https://reviews.llvm.org/D137640


Co-authored-by: Louis Dionne <ldionne.2@gmail.com>