[Bug target/82990] Add -mprefer-vzeroupper

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82990

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 42608
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42608&action=edit
A patch

Sebastian, please take a look.