Summary

When POCO_HAS_UNIX_SOCKET is not defined (e.g., older Windows SDKs lacking afunix.h, or when POCO_NET_NO_UNIX_SOCKET is explicitly defined), the build failed because:

• HTTPSession::connect() referenced SocketAddress::UNIX_LOCAL
• SocketAddress::init() called newLocal() which is only declared when POCO_HAS_UNIX_SOCKET is defined
• WebSocketImpl constructor referenced SocketAddress::UNIX_LOCAL

Changes

1. Net/src/HTTPSession.cpp - Added #if defined(POCO_HAS_UNIX_SOCKET) guard around UNIX_LOCAL check
2. Net/src/SocketAddress.cpp - Added guard around isUnixLocal() and newLocal() call
3. Net/src/WebSocketImpl.cpp - Added guard around UNIX_LOCAL check
4. Net/include/Poco/Net/SocketDefs.h - Use POCO_HAVE_CPP17_COMPILER macro instead of direct __cplusplus >= 201703L check for consistency
5. Data/ODBC/include/Poco/Data/ODBC/ODBC.h - Same consistency improvement
6. Foundation/include/Poco/Platform_POSIX.h - Simplified thread-safe local static init check since POCO requires C++17 (which guarantees this since C++11)

Closes #5064