[Bug target/82942] Generate vzeroupper with -mavx512f -mno-avx512er -O2

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82942

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 42583
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42583&action=edit
An untested patch