[Bug libstdc++/71921] missed vectorization optimization

[arjan at linux dot intel.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71921

--- Comment #2 from Arjan van de Ven <arjan at linux dot intel.com> ---
I tried with <= and it doesn't seem all to eager to be vectorized that way
either; fast-math works either way