[Bug driver/115990] Consider deprecating -Ofast

[gonzalo.gadeschi at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115990

--- Comment #16 from gnzlbg <gonzalo.gadeschi at gmail dot com> ---
Maybe if it was called "-Ounsafe-fast" people may end up reading the docs to
find out what that unsafe means.

If we had that option as an alias to "-Ofast", then maybe -Ofast could just
warn with:

> -Ofast is deprecated, use -Ounsafe-fast instead. If you don't know why -Ofast is unsafe, please do read the documentation here: https://gcc.gnu.org/wiki/FloatingPointMath

That would introduce quite a bit of churn into the SW ecosystem in general, but
at least that warning would be actionable, educational, and anyone getting
burned by -Ounsafe-fast could no longer blame anyone else but themselves.