tuklib_physmem: Silence warning from -Wcast-function-type on MinGW-w64.

tuklib_physmem: Silence warning from -Wcast-function-type on MinGW-w64.

tuklib_physmem depends on GetProcAddress() for both MSVC and MinGW-w64
to retrieve a function address. The proper way to do this is to cast the
return value to the type of function pointer retrieved. Unfortunately,
this causes a cast-function-type warning, so the best solution is to
simply ignore the warning.