[X86] Pre-commit test case for bug in combineShiftRightArithmetic

It has been noticed that combineShiftRightArithmetic isn't dealing
properly with large shift amounts, as demonstrated by the test
case added in this commit.

I think the problem partly is related to X86 using i8 as shift amount
type during ISel. So shift amount larger then 127 may be treated
as negative shift amounts if not being careful.