[Bug c/84628] attribute(warning/error) should be evaluated before optimization

[jay.krell at cornell dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84628

--- Comment #1 from Jay <jay.krell at cornell dot edu> ---
Also occurs with git trunk ef8d0c5bff3c11a5d67617df2f43775f7a26fad2 8.0.1
20180228.