tell cmake that there is no library for dlopen on emscripten (shuts up warnings "emcc: cannot find library "dl"" for projects that add CMAKE_DL_LIBS to the link line)
Fix returning uninitialised memory to C code. flowinfo is a dead field that's unused, scope_id is actually useful but browsers have terrible support for link-local IPv6 addresses so we needn't support it now.
Merge pull request #2759 from NWilson/incoming

fix linker warning and a small bit of uninitialised memory