Fix lossless_cast test on WASM

[alexreinking]

The correctness_lossless_cast failed on WASM in #8948 during fuzzing with the following LLVM internal assertion error:

correctness_lossless_cast: /__w/llvm-wheel/llvm-wheel/src_cache/main/llvm/include/llvm/Support/Casting.h:560: decltype(auto) llvm::cast(const From&) [with To = LoadSDNode; From = SDValue]: Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' failed.

Unfortunately, the seed was not flushed to stdout prior to the failure. This PR is intended to improve error reporting in this case and, ideally, reproduce and fix the error.

[alexreinking]

correctness_oddly_sized_output failed randomly on x86-32-windows (T=x86-32-windows) but the reason why is unclear. Entering the buildbot and manually running the test yields simply "Success!"

[alexreinking]

We couldn't reproduce the failure here, but there's no downside to merging a "flush the seed" patch.