Very tiny code cleanup

Just reordering a few lines and adding a couple newlines. Should be no
functional change, this is just for readability.
Add arg to define_library_dependency for header-only dependencies

This is needed so that define_library_dependency can be used on
MBCoreUtils.
Use define_library_dependency for MBDependsOnMBCoreUtils

MBCoreUtils has already been changed so that header files are copied
into the variant dir as required by define_library_dependency.