Note that this is the bare minimum change for this to compile with GCC 13, based on how this header is used internally etc. It is technically more correct to explicitly include this header in every file that uses it, but that is left as an exercise for the reader.
As in previous versions, libstdc++ in GCC 13 has trimmed internal inclusion of standard headers, necessitating their proper inclusion when used:
https://gcc.gnu.org/gcc-13/porting_to.html
Note that this is the bare minimum change for this to compile with GCC 13, based on how this header is used internally etc. It is technically more correct to explicitly include this header in every file that uses it, but that is left as an exercise for the reader.