[lldb] Use the NativeSock type instead of plain 'int'

This fixes a warning when building for Windows:

    ../tools/lldb/source/Host/common/TCPSocket.cpp:297:16: warning: comparison of integers of different signs: 'int' and 'const NativeSocket' (aka 'const unsigned long long') [-Wsign-compare]
          if (sock != kInvalidSocketValue) {
              ~~~~ ^  ~~~~~~~~~~~~~~~~~~~

Differential Revision: https://reviews.llvm.org/D132841