* Patch GMP to build on GCC15
* Add cstdint include - GCC15 defaults to C23
* Update GMP PATCH_COMMAND to work without a valid git repo
* Set GMP_DIRECTORY_FLAG
GCC 13 requires an explicit #include <cstdint> for the std::uint32_t data type used by this file. Adding this include allows for the whole project to successfully be compiled on GCC 13