Latest macOS 13.3 rolled out LLVM 15 and thus the way `nullptr_t` is
defined within the `libc++`:

https://github.com/llvm/llvm-project/commit/157bbe6aea22e87c822f6cda3cd404b8f657dce4

This seems to require including `/usr/include` with `-isystem` directive
rather than `-I`. Otherwise we get clang miscompilation issues due to
missing `nullptr_t` declaration.