fix PR68976: only add loop close phi for names defined in loop

fix PR68976: only add loop close phi for names defined in loop

        * graphite-isl-ast-to-gimple.c: Fix comment.
        * graphite-scop-detection.c (defined_in_loop_p): New.
        (canonicalize_loop_closed_ssa): Do not add close phi nodes for SSA
        names defined in loop.

gcc/testsuite

        * gcc.dg/graphite/pr68976.c: New test.

Co-Authored-By: Sebastian Pop <s.pop@samsung.com>
From-SVN: r232658