[CMake] Add function add_dumux_all_flags.

The function can be used instead of calling the
add_dune_*_flag functions.
The function is called from add_dumux_test.
(reviewed by bernd)


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@13785 2fb0f335-1f38-0410-981e-8018bf24f1b0