@thakis caught a bunch of implemented flags for which HelpHidden wasn't
removed. This diff ensures that we prevent those issues going ahead.
I initially considered making %lld expand to include
-fatal_warnings, but that would've made testing for desired warnings
more awkward. Hence this approach.
clang-tidy: warning: twine variables are prone to use-after-free bugs [llvm-twine-local]
not useful