fix Android bootimage build

bb86500 was a step in the right direction, but there was a bug that
caused Type_pad fields to be inserted between every other field in for
a derived class when type-maps.cpp was generated, and this led to
miscompilation of e.g. Android's
java.lang.reflect.Constructor.getModifiers.
Merge pull request #226 from dicej/android-bootimage

fix Android bootimage build