Run GCC7 regressions when GCC<7 OR dev tests on
Run GCC7 regressions when GCC<7 OR dev tests on

 - Better/accurate logic to control when open GCC7 regressions are run
 - Moved `co_reduce_string` test to be with other `co_reduce...` tests

sourceryinstitute/opencoarrays,sourceryinstitute/opencoarrays,sourceryinstitute/opencoarrays