[Clang] Add machinery to catch overflow in unary minus outside of a constant expression context

We provide several diagnostics for various undefined behaviors due to signed
integer overflow outside of a constant expression context. We were missing the
machinery to catch overflows due to unary minus.

Fixes: https://github.com/llvm/llvm-project/issues/31643

Differential Revision: https://reviews.llvm.org/D142867