I'm not sure exactly where the disagreement really is. Perhaps when OP said "ensure that the changes were reverted or fixed to support" you were thinking they meant MSVC reverting changes, while I was thinking of GSL doing it instead, in order to "support" specific compiler versions they have on hand at the time to test.

Either way I think we are on the same page in thinking that compilers don't know/care that GSL exists and aren't doing anything special for it, and that's good enough for me.