Fix some errors and warnings when compiling with Clang
Merge pull request #446 from zrax/clang_fixes

Fix some errors and warnings when compiling with Clang
Added plNetCoreDns for async DNS with c-ares.

Eventually to replace the pnAceWin32Dns stuff... eventually.
You probably can't use both of them right now because of differences in
the WSA versions :(
Let CMake handle c-ares
Fix some issues pointed out in review.