Flower fails to link on macOS

[faern]

I'm trying to install the cloudabi tools on my macOS machine. I followed your guide at https://cloudabi.org/run/macos/. I hit the following error while brew was trying to install flower:

==> cmake . -DCMAKE_C_COMPILER=/usr/local/opt/llvm@4/bin/clang -DCMAKE_CXX_COMPILER=/usr/local/opt/llvm@4/bi
==> make
Last 15 lines from /Users/faern/Library/Logs/Homebrew/flower/02.make:
      LabelEchoingServer::Connect(arpc::ServerContext*, flower::protocol::server::ConnectRequest const*, flower::protocol::server::ConnectResponse*)::'lambda'()::operator()() const in handle_test.cc.o
  "typeinfo for testing::Test", referenced from:
      typeinfo for Handle_Constrain_Test in handle_test.cc.o
      typeinfo for Handle_ClientServer_Test in handle_test.cc.o
  "vtable for flower::switchboard::Handle", referenced from:
      flower::switchboard::Handle::Handle(flower::switchboard::Directory*, flower::switchboard::TargetPicker*, flower::switchboard::WorkerPool*) in handle_test.cc.o
      flower::switchboard::Handle::~Handle() in handle_test.cc.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang-4.0: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [flower_unittests] Error 1
make[1]: *** [CMakeFiles/flower_unittests.dir/all] Error 2
make: *** [all] Error 2