[InstCombine] add rotate narrowing tests with odd types; NFC

[InstCombine] add rotate narrowing tests with odd types; NFC

There's a potential miscompile here. It's unlikely in the real
world because this transform is guarded with shouldChangeType(),
but this test file doesn't include a standard data-layout for
some reason (despite including a custom 1), so we can see the bug.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346966 91177308-0d34-0410-b5e6-96231b3b80d8