Thank you for your question.
In Unix, and I think MinGW too, you should be able to build fuzzylite in 64bit passing the option
-m64 to the compiler. However, most likely you will have to remove the
-Werror flag as there are some warnings being raised when returning
std::vector::size_t as an
int from some methods. The
-Werror flag converts warnings to errors. Let me know if this helps.