Fortify_source and stack-protector-strong

[Florian Weimer]

* Reinoud Koornstra:

> One more question, for FORTIFY_SOURCE=2, can I use either -O1 or -O2
> optimization flags?  I noticed it doesn't like -Os. Thanks,

Historically, I think the expectation was that 1 should be used with -O1
and 2 with -O2.  But I think the required passes run at -O1 as well.

Thanks,
Florian