Compiling Mozc is a really just as hard as Chromimum, so I don’t recommend to try it now, I haven’t finished doing all the build system related work for Mozc.
fcitx-m17n is quite a lot simple, just use the regular way to compile it:
mkdir build cd build; cmake .. -DCMAKE_INSTALL_PREFIX=`fcitx4-config --prefix` make sudo make install
They are both on github:
http://github.com/fcitx/mozc (a pseudo fork, for the reason, check the read me.)
You will need fcitx from git.