[Bug c/70255] change of the order of summation of floating point numbers despite no-associative-math

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70255

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
We'd likely want to warn in merge_decls for this case.