__builtin_constant_p used to be short-cut evaluated to false when building with -O0. This is undesirable as it means that constant folding in the front-end can give different results than folding in the back-end. It can also create conditional branches on constant conditions that don't get folded away. With the improvements to the llvm.is.constant handling on the LLVM side, the short-cut is no longer useful.
Adjust various codegen tests to not depend on the optimizations.