x11/nxcomp: Fix build with Clang 6

Loop.cpp:6751:61: error: invalid operands to binary expression ('__bind<int &, sockaddr *, unsigned long>' and 'int')

if (bind(proxyFD, (sockaddr *) &tcpAddr, sizeof(tcpAddr)) == -1)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~

/usr/include/c++/v1/system_error:577:1: note: candidate function not viable: no known conversion from 'bind<int &, sockaddr *, unsigned long>' to 'const std::1::error_code' for 1st argument
operator==(const error_code& x, const error_code& y) _NOEXCEPT
^

http://beefy12.nyi.freebsd.org/data/head-amd64-default/p473790_s335878/logs/nxcomp-3.5.0.32.log