In Exact SIV and Exact RDIV tests, there are multiple `APInt` arithmetic
operations which can overflow. These overflows are currently not
checked, which may lead to incorrect analysis results. However, adding
overflow checks for each operation can clutter the code and make it
harder to read.
This patch introduces a new wrapper class `OverflowSafeSignedAPInt` that
encapsulates a `std::optional<APInt>` and provides arithmetic operations
with built-in overflow checking. If an arithmetic operation overflows,
the internal `std::optional<APInt>` is set to `std::nullopt`, indicating
an invalid result. Also, if any operand of an arithmetic operation is
invalid, the result will also be invalid. By using this wrapper class in
the Exact SIV and Exact RDIV tests, now overflows are handled properly
while keeping the readability of the code.
Fixes the test added in #171990.
80f3c0db90