I have been using OpenModelica for a while.  I would like my OpenModelica version updated reasonably frequently.  I always compile the source tree (obtained from read only Git repo.)  on my Linux box.

What is the optimal procedure to reduce build time?
Is it necessary to use   --without-omc  flag every time the OMCompiler is updated? 
I use "git submodule foreach --recursive "git pull" to update my sources.
Can I avoid "make clean" to reduce the build time?  ... because only few sources files would have changed.

Some pointers will be much appreciated.