r191394 - Produce an error for unknown -f options.

[Rafael Espíndola]

>> Err, we aren't ready for this. If we're going to do this, could you stage
>> it such that the gcc flags are added but ignored, then we error on unknown
>> options?
>
>
> This is already how it works.  If our list of ignored gcc -f flags isn't
> complete enough, that's simple to fix.

I am happy to revert if needed, but as Eli pointed out adding ignored
options is really easy. Do you have a list?

Cheers,
Rafael