Enhance and use POSIX socket compatibility layer (#2046)

Enhance and use POSIX socket compatibility layer (#2046)

Implement portable wrappers around most socket-related functions, named
x[function], and use them in all callsites.

winsock's socket-related functions are very similar but not
identical to the POSIX standard. Make the mswindows
compatibility layer available to MinGW, and modernize it.

Error highlighting the issue:
```
TcpAcceptor.cc: In member function
  'bool Comm::TcpAcceptor::acceptInto(Comm::ConnectionPointer&)':
TcpAcceptor.cc:352:17: error:
  comparison of unsigned expression in '< 0'
  is always false [-Werror=type-limits]
  352 |     if (rawSock < 0) {
```