Detailed process here, in Bahasa Indonesia.
This only covers the compiling stuff:
$ git clone http://git.rockbox.org/rockbox
$ mkdir rockbox/bangun && cd rockbox/bangun
$ ../tools/configure --eabi --ram=180MB --target=android
$ make -j4 && make zip && make apk
Voila, the APK is ready. Note that on my original entry the RAM was set to 256. Actually, I made a bet to set it to 180MB. I made the bet for Commtiva Z71/Nexian Journey/Boston Mania phone. I think that’s the memory available according to Settings–>About.
For those of you that unable to compile the thing or just want the APK, click here. I have put it in 4shared. [RANT: I wished I could put it in IDWS, but it kept bitching about asking my REAL NAME, ADDRESS, and a policy that let them do what they want with my PROFILE.]