Fix underflow in Triton's highestPowOf2Divisor function when the input is INT_MIN

[Moerafaat]

highestPowOf2Divisor function here:
https://github.com/triton-lang/triton/blob/8e63999da7ef87fc6ac908f26a9b9c05ce85ab70/include/triton/Dialect/Triton/IR/Utility.h#L33

will run during analysis when coalesce pass is invoked. This function will underflow if the given input is INT_MIN and will fail when run under ASAN.
This change handles this edge case and adds a minimal lit test to make sure the case is covered.

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