darwin: minimal SDK lacks socket and process link symbols

Darwin socket programs need libSystem symbols that the minimal SDK does not declare. This blocks the native socket path used by my CLI.

Build the direct syscall test from #5636 with tinygo build testdata/darwinsockets.go on Darwin. Calls such as syscall.Socket, Bind, and Listen need _socket, _bind, and _listen. The program should link and complete its loopback connection.

Source checked on 18 September 2026. dev at 93940cb6 still lacks these declarations. The process proposal #5634 also needs posix_spawn declarations from the same library.

#5636 closed on 17 September with a request for this issue. This covers link declarations. #5604 and #5612 cover Darwin call trampolines. The 14 September review on #5612 also identified missing socket stubs. tinygo-org/net#74 covers the host network device.

Replacement draft PR #5701.