Code improvement for iowin32.c

[Lwisce]

I found that in the iowin32.c, there are some function parameters and declared variables that are not used. This will generate warnings in the MSVC compiler. Can we consider using (void) for unused function parameters and directly deleting unused variables to avoid warnings? Here is example:

voidpf ZCALLBACK win32_open64_file_func(voidpf opaque, const void filename, int mode) { - const char mode_fopen = NULL; + (void)opaque; DWORD dwDesiredAccess,dwCreationDisposition,dwShareMode,dwFlagsAndAttributes ; HANDLE hFile = NULL;

[madler]

Ok. Warnings averted.