Cannot build 4.0.3 with clang

[drook]

Cannot build swiften with clang 8.x:

Build invoked as:

./scons V=1 swiften_dll=1 boost_bundled_enable=false boost_libdir=/usr/local/lib Swiften SWIFTEN_INSTALLDIR=/usr/local/swiften /usr/local/swiften

Boost: 1.72.0_2
Clang:

FreeBSD clang version 8.0.1 (tags/RELEASE_801/final 366581) (based on LLVM 8.0.1)
Target: x86_64-unknown-freebsd12.1
Thread model: posix
InstalledDir: /usr/bin

Crash:

Swiften/Network/PlatformNATTraversalWorker.cpp:160:58: error: invalid operands to binary expression
      ('basic_ostream<char, std::__1::char_traits<char> >' and 'boost::logic::tribool')
    SWIFT_LOG(debug) << "UPnP NAT traversal supported: " << miniUPnPSupported << std::endl;
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~