Allow build of mkl roll from same source as intel.
Bug fix: replace hard-coded value with make var ref.
Merge pull request #2 in APS/intel-roll from feature/build-mkl-roll-from-same-source to master

* commit 'd9805ce2d066dbf432d67bc868601158509a54c5':
  Bug fix: replace hard-coded value with make var ref.
  Allow build of mkl roll from same source as intel.