MSYS2+MinGW-W64 x86.64 compile error on handler.cc

[Raphael Kim]

Compile error occured as :

handlers.cc: In function 'int Add_fd(lua_State*)':
handlers.cc:237:26: error: invalid conversion from 'void (*)(int, void*)' to 'Fl_FD_Handler' {aka 'void (*)(long long unsigned int, void*)'} [-fpermissive]
     Fl::add_fd(fd, when, FdHandler, (void*)L);
                          ^~~~~~~~~
In file included from internal.h:47,
                 from handlers.cc:26:
C:/msys64/usr/local/include/FL/Fl.H:463:54: note:   initializing argument 3 of 'static void Fl::add_fd(int, int, Fl_FD_Handler, void*)'
   static void add_fd(int fd, int when, Fl_FD_Handler cb, void* = 0); // platform dependent
                                        ~~~~~~~~~~~~~~^~
make: *** [<builtin>: handlers.o] Error 1

[Raphael Kim]

Fixed compile error on fd8bea5..555ddfa