Use SESES as the fallback at O0 where the optimized LVI pass isn't desired due
to its effect on build times at O0.
I updated the LVI tests since this changes the code gen for the tests touched in the parent revision.
This is a follow up to the comments I made here: https://reviews.llvm.org/D80964
Hopefully we can continue the discussion here.
Please add a comment here to clarify that if getOptLevel() == CodeGenOpt::None then SESES will provide mitigation when LVILoadHardening is enabled.