Avoid linking libdl on emscripten. Closes GH-33
Avoid linking libdl on emscripten. Closes GH-33

Note that both EMSCRIPTEN and UNIX are true when targeting emscripten,
so if only the first conditional is modified then dl would be added
anyway. Keep it on UNIX but not if EMSCRIPTEN.

satoshinm/NetCraft,satoshinm/NetCraft,satoshinm/NetCraft,satoshinm/NetCraft,satoshinm/NetCraft