Also remove text saying /O1 and /O2 implies /Gs. They don't seem to do that, at least with modern MSVC (see bug).
https://docs.microsoft.com/en-us/cpp/build/reference/gs-control-stack-checking-calls?view=vs-2017 still claims that /Gs is /Gs0 though. Is that just wrong? https://bugs.llvm.org/show_bug.cgi?id=39074#c2 suggests it is. Should we ask bruce to file a doc bug?
And since this flag is supposed to get the default behavior, should it be a CLIgnoredFlag instead of duplicating the 4096 somewhat redundantly?
I've submitted feedback on the document page: https://github.com/MicrosoftDocs/cpp-docs/issues/445
By not ignoring it, we enable using /Gs to override a previous e.g. /Gs0 flag, which I think is the correct thing to do.