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/fcitx-m17n

http://github.com/fcitx/mozc (a pseudo fork, for the reason, check the read me.)

You will need fcitx from git.

Have fun!