[RISCV] Add another test showing incorrect BUILD_VECTOR lowering

This test shows a (contrived) BUILD_VECTOR which is correctly identified
as a sequence of ((vid * -3) / 8) + 5. However, the issue is that using
shift-right for the divide is invalid as the step values are negative.

This patch just adds the test: the fix is added in D123796.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D123989