This is a bugfix. Simply put, 2u - 1u != 2u - 1u. See the static
assertion in the test file. The fix simply ban the negation of unsigned
expressions. This way the we are getting a little bit more conservatie,
but at least we do not infer wrong values.
Actually, this test case was correct, because UINT_MID is a special value and for that
_Static_assert(UINT_MID == -UINT_MID, "");