Warnings on Windows GCC in header code

This is similar to the previous issue but on Windows GCC,

https://github.com/correaa/boost-multi/actions/runs/10067263974/job/27830388396?pr=56#step:4:8634
```
gcc.compile.c++ bin.v2\libs\boost-multi\test\zero_dimensionality.test\gcc-8\release\x86_64\cxxstd-2a-iso\link-static\threadapi-win32\threading-multi\visibility-hidden\zero_dimensionality.o
In file included from ./boost/test/included/unit_test.hpp:20,
from libs/boost-multi/test/zero_dimensionality.cpp:25:
./boost/test/impl/debug.ipp: In instantiation of 'void boost::debug::{anonymous}::dyn_symbol(T&, const char*, const char*) [with T = int (*)()]':
./boost/test/impl/debug.ipp:167:72: required from here
./boost/test/impl/debug.ipp:143:11: error: cast between incompatible function types from 'FARPROC' {aka 'long long int (*)()'} to 'int (*)()' [-Werror=cast-function-type]
res = reinterpret_cast( ::GetProcAddress( m, symbol_name ) );
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```