Recover some lost EH performance on Unix amd64 (#90033)

Recover some lost EH performance on Unix amd64 (#90033)

* Improve EH performance on Unix amd64

Few months ago, a change to enable AVX512 on Unix was merged in.
That change has enlarged the CONTEXT structure significantly and
it was found that it has caused 6..17% regressions in exception handling
microbenchmarks.

This change gets some of the lost performance back by adding custom
copy constructor and assignment operator to the CONTEXT structure
and preventing copying of the AVX / AVX512 stuff if the source
context doesn't have it. I have observed 3..9% gain on my machine.

Close #84308

* Fix gcc build and size for non-xstate case

* Fix yet another gcc break

* Fix build break

* Revert the gcc fixes and disable the warning

The zeroing of CONTEXT structure is used at too many places and
it is valid, so rather than trying to modify all the places by
using placement new, just disable the warning for gcc.