Windows support via MSYS mingw-w64-ucrt-x86_64

[alex-Symbroson]

This merge request relates to #142, #123 and, fundamentally, #23

It fixes compilation issues on Windows, specifically MSYS builds with the mingw-w64-ucrt-x86_64-gcc compiler and the related toolchain.

The changes can be broken down to the following:

• casting -1 error states for NativeSocketType
• linking against ws2_32.dll
• allowing unsafe function pointer casts in wepoll.c

Requirements:

• Install MSys
• Install toolchain

packman -Syuu
pacman -S  mingw-w64-ucrt-x86_64-gcc  mingw-w64-ucrt-x86_64-cmake  mingw-w64-ucrt-x86_64-make
# optional
pacman -S  mingw-w64-ucrt-x86_64-openssl

Build instructions:

mkdir build
cd build
cmake -G "MinGW Makefiles"
mingw32-make.exe

Test output:

seasocks\build> .\src\test\c\AllTests.exe       
===============================================================================
All tests passed (66040 assertions in 83 test cases)

Toolchain:

C:\msys64\ucrt64\bin\cmake.exe --version
cmake version 3.31.4
CMake suite maintained and supported by Kitware (kitware.com/cmake).

C:\msys64\ucrt64\bin\g++.exe --version  
g++.exe (Rev2, Built by MSYS2 project) 14.2.0
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

C:\msys64\ucrt64\bin\mingw32-make.exe --version        
GNU Make 4.4.1
Built for Windows32
Copyright (C) 1988-2023 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.