Revert "Remove -fopenacc command line option"

[ronlieb]

Reverts #187

[ronlieb]

thanks Dan, this will help with reducing lots of lit test conflicts and openacc going forward

[dpalermo]

I have created a smaller patch that reapplies the flag change but instead skips related tests by using lit.cfg excludes instead of deleting all of the unsupported tests. We also decided not to commit it on ATD to avoid increasing the delta at a time we are trying to shrink it. Instead, we will apply it as one of the additional patches on the AFAR so the desired behavior is seen by customers.