Fix Android CFLAGS

Kill the NDEBUG define, which we're not using anywehere else.
zmq & co default to building w/ -Wall + -Werror, and use some
variables only in assert calls whose definition aren't ifdefed
around NDEBUG, so leaving it defined leads to stupid build failures.
Merge pull request #205 from NiLuJe/master

Fix Android CFLAGS