See http://stackoverflow.com/questions/24194961/how-do-i-use-setsockoptso-reuseaddr
Compiling juce_core.cpp
In file included from ../../../../modules/juce_core/juce_core.cpp:150:0:
../../../../modules/juce_core/network/juce_Socket.cpp: In member function ‘bool juce::DatagramSocket::setEnablePortReuse(bool)’:
../../../../modules/juce_core/network/juce_Socket.cpp:707:25: error: ‘SO_REUSEPORT’ was not declared in this scope
const int optname = SO_REUSEPORT;
I guess I need to change my section reading order! I just replied about this in, first, Android, then General.
It seems the whole thing stemmed from someone trying to run two instances of an app on OS X, then thinking SO_REUSEADDR wasn't working, but adding SO_REUSEPORT seemed to fix it (I would have actually expected the datagrams to just go to one instance).