If you just use one Marc version, simply select DAMASK_marc.f90, this matches for all releases.
DAMAKS_marc.marc compile with Marc 2010 does not work with Marc 2012. In case you need more than one Marc version in parallel, run symLink_Code.py in /code/setup to generate symlinks for Marc version 2010,2011,2012
DAMASK_marcXXXX.f90 now is not a copy any more but contains one definition and an include statement
setup_code of spectral solver is now replaced by the standard 1) configure 2) make 3) make install