Simplify Gaussian pencil code
Simplify Gaussian pencil code

Cast allocated memory to VLA, to allow indexing the same way as the
PENCIL version.


Former-commit-id: 016063fd57d0d572c510023bb4ee4799de5b4d5b
pencil-language/pencil-benchmark,dividiti/pencil-benchmark,rbaghdadi/pencil-benchmark,rbaghdadi/pencil-benchmark,dividiti/pencil-benchmark,pencil-language/pencil-benchmark,pencil-language/pencil-benchmark,dividiti/pencil-benchmark,rbaghdadi/pencil-benchmark