CMake build doesn't support OS X

Couple problems:

libm, librt, and libdl are all Linux specific, and provided "for free" on OS X

CppUnit (at least on OS X) needs `-std=c++11`

clang's ld doesn't understand --wrap

I can post an easy patch that at least lets you build the client (but not the tests). The tests use that `--wrap` and it's non trivial to fix that on OS X.