Followup to #27447.
See https://releases.llvm.org/16.0.0/projects/libcxx/docs/DesignDocs/DebugMode.html:
Libc++ provides a debug mode that enables special debugging checks meant to detect incorrect usage of the standard library. These checks are disabled by default, but they can be enabled by vendors when building the library by using LIBCXX_ENABLE_DEBUG_MODE.